jshs

Journal of Steroids & Hormonal Science

ISSN - 2157-7536

Review Article - (2011) Volume 2, Issue 2

Innate Immunity in the Lower Female Mucosal Tract

Miranda A. Farage1*, Kenneth W. Miller1, G. Frank Gerberick1, Felipe H. Saito2, William J. Ledger3 and Steven S. Witkin3
1The Procter and Gamble Company, Cincinnati, OH, USA
2Department of Gynecology and Obstetrics, Botucatu Medical School, Sao Paulo State University, UNESP, Botucatu, Brazil
3Department of Obstetrics and Gynecology, Weill Medical College of Cornell University, New York, USA
*Corresponding Author: Miranda A. Farage, PhD, Feminine Clinical Sciences, The Procter & Gamble Company, Winton Hill Business Centre, 6110 Centre Hill Rd, P.O. Box 136,Cincinnati, OH 45224, USA, Tel: (513) 634-5594, Fax: (866) 622-0465 Email:

Abstract

The moist, nonkeratinized surfaces of mucosal tissues face a significant challenge with regard to protection of internal tissues from pathogenic invaders, a situation augmented by the fact that these sites are colonized by commensal microorganisms. The mucosa of the human reproductive tract is unique in that it must also balance the need for immunologic vigilance against pathogenic microorganisms and neoplastic cells with its critical role in reproduction, successfully creating an immune environment that tolerates allogeneic spermatozoa as well as the semi-allogeneic developing fetus. This article reviews the components of innate immunity that are functional in the cervicovaginal environment.

Keywords: Humoral immunity; Innate immunity; Bacteriocins; Cell mediated immunity; Defensins; Mucosal tissue; Commensal microorganisms; Cervicovaginal environment.

Introduction

The female reproductive tract consists of a series of cavities lined by a highly vascular and glandular tissue called the mucosa. Mucosal tissues, nonkeratinized epithelia derived mainly of endoderm lined in epithelium, cover the surfaces of numerous body cavities, providing a moist interior lining which provides a hospitable habitat for a rich and dynamic microflora.

The mucosa of the female reproductive tract is unique in that even though it must, like all mucosal surfaces, maintain a vigilant and vigorous immunity against pathogenic intruders [1], it must also maintain an environment favorable to the reproductive process, tolerating the presence of allogeneic spermatozoa in the vagina, permitting their migration to the Fallopian tubes, and facilitating implantation of the semi-allogeneic fertilized ovum [2].

The ultimate goal of the lower female genital tract immune system is thus to effectively combat pathogens while at the same time modulate immune function in order to optimize fertility [3]. This delicate balance is accomplished by a complex interplay of local humoral, cell-mediated, and innate immunity [3].

Innate immune system defenses do not recognize single microbial epitopes and can therefore eliminate microorganisms rapidly, without the 3 to 5-day delay involved in mounting an antigen-specific response [4]. Bacterial cells or components of bacterial cell walls are nonspecifically recognized by innate immune factors which then eliminate the potential pathogens by multiple mechanisms, including antimicrobial factors secreted by local epithelial cells, ingestion by resident phagocytes, and activation of an inflammatory response [4].

Innate defenses, while common to all women, can nonetheless vary. Genetic polymorphisms specific to individual hosts can compromise the ability to mount an effective innate immune response in the vagina and thus increase susceptibility to sexually transmitted diseases [5]. For example, variations in the ability to produce adequate levels of interleukin-1 receptor antagonist and Toll-like receptor (TLR)-4 have been shown to influence the bacterial composition of the vagina [6,7]. Observed racial differences in composition of the endogenous microflora may also be attributable to the incidence of genetic polymorphisms in a given population [8].

Adaptive immune processes in the lower genital tract involve both B and T lymphocytes and their products, which recognize specific components of individual microorganisms [9].

Humoral immunity consists of B cells that secrete antibodies. Antibodies bind to microbial cells (thus preventing their entry into host cells), coat pathogens to induce phagocytosis, and stimulate other immune responses such as the complement pathway [10]. Components of humoral immunity are displayed in table 1.

Antibody Source Action
IgA Secretory IgA produced by mucosal tissues and fallopian tubes [67] Inhibits microbial adherence to surfaces
Agglutinating resident microbes [68,69]
    Reducing the hydrophobic nature of the microbes [70]
    Blocking microbial adhesions [71]
    Rendering viruses ineffective. Aggregating virus particles [72]
    Neutralizing microbial toxins and enzymes.  Blocking binding to target cells [73]   
    Inhibiting penetration of antigen into the mucosa.  Binding soluble antigens and facilitating removal by mucus flow [68]
    Opsonization of microbes for mucosal phagocytes.  Coating pathogen with IgA [68]
    Stimulating antibody-assisted cell-mediated immunity.  Inducing complement-independent antibacterial action of monocytes [74]
    Augmenting T-cell antimicrobial activity (specifically against T cells) [75]
    Promoting activity of innate immunity [76]
    Increasing microbe trapping of mucin by mimicking microbe receptor sites [77]
IgG Transudate from blood stream [67]
Actively transported [78]
Locally produced [79]
Direct action against bacteria and viruses.  Immune exclusion of HIV particles [80]; binding, agglutination of bacteria,  complement activation [81]   

Ig = immunoglobulin

Table 1: Components of Humoral Immunity in the Lower Female Reproductive Tract.

Cell-mediated immunity consists of various subsets of T lymphocytes which act in conjunction with other cytotoxic cells. Cellmediated immunity in the lower genital tract eliminates primarily intracellular bacteria as well as virus-infected and tumor cells either by stimulating phagocytosis or by the direct action of cytotoxic, or natural killer (NK) and antibody-dependent killer (K) cells. Cytotoxic T cells (CD8+) kill virus-infected cells; stimulatory cells (CD4+) activate other types of cells including macrophages and B cells [9]. Components of cell-mediated immunity are displayed in table 2.

Cell Type Distribution Action
Langerhans/
dendritic cells
Abundant in vaginal and cervical mucosa Present antigen to T cells (adaptive); phagocytize bacteria or virus particles (innate) [11]
Neutrophils Abundant throughout female genital tract Produce antipathogenic chemokines and cytokines (innate) [50]
T cells Abundant within mucosal-associated lymphoreticular tissue within the lamina propria of cervix Direct cytotoxic action(innate) or stimulation of other immune responses (adaptive) [11]
  • CD8+
Most common epithelial T cells in FGT, cytotoxic Kill virus- infected cells (adaptive) [82]
  • CD4+
Less common, Stimulatory Activate macrophages, B cells (adaptive) [82]  
NK cells Throughout FGT Kill virus-infected host cells (adaptive and innate mechanisms)[83]
Macrophages Abundant within mucosal-associated lymphoreticular tissue within lamina propria of cervix; most abundant phagocytes Present antigen to T cell (adaptive) [11]

FGT = female genital tract; NK = natural killer

Table 2: Components of Cell-Mediated Immunity in The Female Lower Reproductive Tract.

Mucosa of the Female Reproductive Tract

The female reproductive tract is subdivided into three major compartments: the lower genital tract (comprised of the vagina and cervix), the transitional endocervix, and the upper genital tract (comprised of the endometrium and the Fallopian tubes) [11]. The lower reproductive tract is populated by a rich commensal microflora, abundant in anaerobic microbes [12], which blanket the surface of the vagina and ectocervix and assist in limiting the growth of more virulent microorganisms [1]. In most healthy reproductive age women, this population is dominated by Lactobacillus or other acid-producing species [8,11,13,14].

The mucosal surface of the female genital tract is an intricate and dynamic biosystem containing multiple innate and acquired immune system components that provide an effective barrier to external pathogens and is therefore adapted in each area of the genital tract to the particular local needs. The endometrium as well as the endocervix is lined by a single-cell layered columnar epithelium which secretes mucus. Endocervical tubular glands and deep invaginations of the surface epithelium increase the surface area available for mucusproducing cells [15]. The secretory activity of the endocervical glands is regulated by estrogens [16].

The endocervix is a transition zone, where the columnar epithelium of the endometrium and endocervix meets the squamous epithelium of the cervix, the entry to the lower genital tract. The cervix as well as the ectocervix is lined by non-keratinized, stratified, squamous epithelium that sits atop a thick lamina propria and vascular submucosa and that continues into the vaginal epithelial layer.

The vaginal wall consists of three layers, an inner layer of fibrous connection tissue, a middle muscular layer, and an outer layer of mucosa, lubricated by secretions of the cervical glands.

The vaginal mucosa, in contrast to other mucosal surfaces that contain squamous epithelia that began as columnar in the developing fetus, lacks subdermal secretory glands; nevertheless it maintains significant secretory capacity through a network of intercellular pathways, making the entire vaginal surface a secretory structure [17]. The epithelial cells of the vagina also contain large numbers of estrogen receptors which respond to estrogen stimulation [16]. The ectocervix is structurally and immunologically similar to the vagina.

Throughout the female genital tract a mucus blanket coats the nonkeratinized epithelia, providing a formidable semi-permeable protective barrier to the exposed epithelial surface [18].

Components of Innate Immunity in the Female Genital Tract

Epithelial cells barrier

Organisms which manage to navigate their way through the mucus blanket that covers the vaginal surface will eventually reach the vaginal epithelia. The maturation and proliferation of the epithelium is under hormonal control, with maximum thickness occurring during peak levels of circulating estrogen [19]. In addition, the lower reproductive tract mucosa is unique in that it is responsive to both the direct and indirect effects of sex hormones. It responds directly to estrogen stimulation as well as to the cytokines and growth factors also stimulated by estrogen and produced by fibroblasts and migratory cells in the reproductive tract, enabling the lower female genital tract to exquisitely balance both immune and reproductive functions [20].

The cervicovaginal epithelium, together with its tissue-associated phagocytes (macrophages and neutrophils), represent the first line of cellular microbial defense to provide a physical and chemical barrier and act as sentinels, inducing other immune responses through the production of cytokines and chemokines [9]. Epithelia play an important role in innate immunity by 1) providing a mechanical barrier to pathogen entry, 2) inducing death of infected cells by necrosis, apoptosis, or phagocytosis, 3) releasing protective cytotoxic substances, 4) producing a wide variety of signals of cell injury (e.g., chemokines, cytokines, prostaglandins, heat shock proteins) that both attract and activate leukocytes, 5) initiating and amplifying an acute inflammatory reaction, and 6) activating both humoral and cell-mediated immunity [12].

Rapid innate defenses against microbial infection necessitate a broadly specific recognition of invading bacteria, fungi, parasites, and viruses as well as endogenous ligands associated with cell damage [12]. Epithelial cells recognize specific patterns in the arrangement of conserved key molecules on the surface called microbe-associated molecular patterns (MAMPs) which include lipopolysaccharide (LPS), lipoproteins, peptidoglycans, lipoarabinomannans and oligosaccharides.

The MAMPs are recognized by pattern recognition receptors (PRRs) which are widespread on a wide variety of immune cells, particularly those involved in innate immunity (macrophages, neutrophils, dendritic cells) [4], but are also found throughout the mucosal epithelium [21]. One family of PRRs called Toll-like receptors (TLRs) play an important role in innate immunity [12]. Ligation of TLR by microbial products results in induction of an inflammatory immune response characterized by the production of cytokines and antimicrobial factors and resulting in facilitation of adaptive immune responses [22].

Toll-like receptors are transmembrane proteins which have in common similar structures All TLRs include first a cytoplasmic signaling domain. This domain is separated by a single, membranespanning domain from a third domain, a ligand-recognition domain. The ligand-recognition domain contains 19 to 25 copies of leucine-rich repeats, and provides a highly specific binding surface for the cognate ligand [23].

Ten different TLR receptors have been identified in the lower genital tract of human females; each responds specifically to a distinct MAMP [24]. TLRs are designed to recognize, with high specificity, various proteins, lipids, carbohydrates, and nucleic acids of invading microorganisms and are typically located on either plasma membranes or intracellularly. (table 3) Recognition produces a rapid response by activating signaling cascades that trigger immune and inflammatory responses involving the production of pro-inflammatory mediators [25] and activation of the acquired immune response (both humoral and cell-mediated) [26].

Receptor Number Expression Recognition site Target Organism
TLR 1 Constitutive expression in epithelial cells of fallopian tubes, endometrium endocervix, ectocervix, vagina, uterine NK cells, vascular endothelial cells, and smooth muscle cells in cervical stroma as well as uterus [12] LPS, PGN, flagellin Bacteria [60,84]
TLR 2 Constitutive expression in epithelial cells of fallopian tubes, endometrium, cervix, vagina, smooth muscle cells of cervix and vagina, endometrial stromal cells, uterine NK cells. Highest levels in fallopian tubes and cervix [12]  LPS, PGN, flagellin (heterodimers in TLR1 or TLR6 complexes recognize microbial components) Bacteria [85,86]
TLR 3 Constitutive expression in tissue samples from fallopian tubes, endometrium, cervix, and vagina. Other expression in epithelial cells of fallopian tubes, endometrium endocervix, ectocervix, and vagina. Also in stromal fibroblasts of vagina, endocervix and in  uterine NK cells [12] Nucleic acids
(ds RNA)
Virus[60,87]
TLR 4 Constitutive expression in fallopian tubes, endometrium cervix, vagina, declines from fallopian tubes to vagina, although presence in epithelial cells debated [12] LPS, heat shock protein 60, glycoinositolphospholipids of protozoa, viral envelope proteins, activates NK and other immune response [84] Bacteria, Virus [84]
TLR 5 Constitutive expression in epithelial cells of fallopian tubes, endometrium, vagina, endocervix [12] flagellin Bacteria [88]
TLR 6 Constitutive expression in epithelial cells of fallopian tubes, endometrium, endocervix, ectocervix, vagina, uterine NK cells and stroma fibroblasts in vagina [12] LPS, PGN, flagellin Bacteria [12]
Fungi [60]
TLR 7 Constitutive expression in epithelial cells of fallopian tubes, endometrium, cervix, vagina, uterine NK cells and endometrial stroma [12] Nucleic acid (ss RNA) Virus [23,89]
TLR 8 Constitutive expression in epithelial cells of fallopian tubes, endometrium, cervix, vagina, and endometrial stroma [12] Nucleic acid
(ss RNA)
Virus [23]
TLR 9 Constitutive expression in epithelial cells of fallopian tubes, endometrium, cervix, vagina, and endometrial stroma [12] Nucleic acid (unmethylated deoxytidyl-phosphate-deoxyguanosine components of both bacterial and viral genomes) Bacteria and viruses [90]
TLR 10  Constitutive expression in fallopian tubes, human NK cells; possibly in endometrial epithelia and stroma [12,91] Ligand unknown Recognition unknown [12]

ds = double-stranded; LPS = lipopolysaccharide; NK = natural killer; PGN = peptidoglycan; RNA = ribonucleic acid; ss = single-stranded; TLR = toll-like receptor

Table 3: Role of Toll-Like Receptors in the Lower Female Reproductive Tract.

Expression of TLRs, however, vary widely at different sites in the lower genital tract. Endometrial epithelial cells express TLRs 1-6, and 9; endocervical cells express TLRs 1-3, and 6 but not 4 or 5. TLRs 2 and 4 levels of expression vary widely. TLR 4 is not expressed by cervical or vaginal epithelial cells [27]. These studies suggest that the differential expression of Toll-like receptors in the female reproductive tract may be distributed in such a way as to maintain commensal microbial populations [28].

TLR expression is modulated by estrogen levels, with higher levels of expression of TLRs 2, 3, 4, 5, 6 , and 9 during the secretory phase as compared to other phases [12,29]. It has also been observed that the declining levels of estrogen after menopause are associated with a loss of TLR expression [30].

Although each TLR has a specific ligand, together they are collectively able to respond to a wide variety of bacterial, viral, fungal, and parasitic components. TLRs mediate the activation of epithelial cells by microbial products and may also regulate expression of antimicrobial peptides by epithelial cells [31]. The cervicovaginal environment has an ongoing need to appropriately respond to pathogens yet avoid a continual immune response to commensal organisms which would result in chronic inflammation. TLRs , with their specific ligand recognition across a wide variety of epithelial and immune cells provide a unique and diverse mechanism for pathogen recognition, allowing cells to recognize a wide range of MAMPs and create an immunological tolerance of commensal organisms in the lower genital tract but a nearly absolute intolerance of commensal flora in the endometrium and Fallopian tubes, thereby keeping the uterine environment sterile and avoiding immune responses which would jeopardize reproductive function [12].

The function of other intracytoplasmic PRRs, NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs) remain to be characterized in the female genital tract.

Mucus

Apical epithelial cells also produce a hydrophilic layer of glycoprotein called glycocalyx that hydrates the luminal surface and covers it with a mucus blanket [1,11]. This mucus acts as a protective barrier, not only blocking the spread of microbes from the vagina into the endometrial cavity, but also by concentrating a variety of pathogenfighting products [32]. Commensal organisms often use “hold fast” mechanisms that operate well in viscous fluids in order to remain in the tissue surface ecosystem; successful pathogens find ways to disrupt the mucus blanket and gain access to the epithelial cell surface [33].

One property of the mucus layer that contributes to defense is the ability to maintain an undisturbed layer of mucus at epithelial surface, even under provocation such as copulation [34]. Viscoelasticity prevents nearly all bacteria from reaching the epithelial surface, although some small viruses move readily through [34]. The glycocalyx, a highly viscous layer composed of cell-surface mucins anchored in the cell membrane and combined with secreted mucin fibers, is packed more closely and forms a final imposing barrier to prevent pathogen adherence [34].

The thickness of the mucus blanket is determined by the balance between the rate of secretion and rate of degradation and shedding. The gastrointestinal (GI)-tract mucus blanket varies between 50 and 450 μm in thickness [34]. Most foreign particulates, including conventional particle-based drug delivery systems, are efficiently trapped in human mucus layers by stearic obstruction and/or adhesion. Bacteria have great difficulty in accessing mucus-covered tissues, especially if the mucus blanket is thick and is moving at a considerable speed across the tissue surface [34].

Cervical mucus provides a physical barrier by creating a concrete interface between the internal and external environment, serving as the outermost fortification against foreign pathogens, toxins, and environmental particles [18]. Mucus contains largely water and glycoproteins called mucins [11] which create a heterogeneous mesh network of cross-linked bundles and entangled mucin fibers [18] in a watery interstitial fluid [35]. Though long believed to provide primarily a steric barrier, it has been recently recognized that mucus actually contains pores much larger than the diameter of most viral pathogens (pores as big as 1800 nm in diameter versus 100 to 200 nm for the virus particle) [35], with entrapment of the potential pathogens more a function of microadhesion than steric obstruction [35]. Entrapment by microadhesion provides rapid selective passage of some proteins and particles [18]. The capacity of bacteria to degrade mucin molecules is a substantial predictor of its invasive potential [35].

The mucus layer is continually secreted and shed [35], and most of the time is about 2000 times more viscous than water. As ovulation approaches each month, however, its viscosity decreases by about 95% [18], a substantial modulation of the cervicovaginal environment reflecting its hormonal control [36].

Commensal microflora

A primary component of the vaginal fluid are commensal microorganisms [17]. The microflora of most women is dominated by Lactobacilli or other acid producers; other common commensals include Gardnerella vaginalis, coagulase-negative Staphylococci, Enterococcus spp, Ureaplasma urealyticum, and Escherichia coli [37]. The presence of commensal microflora is known to have inhibitory effects with regard to significant growth of non-commensal organisms. This can be traced to at least four aspects of commensal populations: production of an acidic vaginal milieu, production of hydrogen peroxide, competition by commensal bacterial for adherence to the vaginal epithelia and production of antimicrobial products.

During the reproductive years, desquamated vaginal epithelial cells release glycogen which is commonly degraded by Lactobacillus, creating an acidic milieu which acts to restrict the growth of pathogenic microorganisms [38]. Lactobacilli metabolize glycogen, released by vaginal epithelial cells, into lactic acid, which in turn renders vaginal fluid acidic (pH 3.5 to 4.7) [11]. Lactic acid and low pH of vaginal fluid has been shown to exert selective antimicrobial activity against nonresident species of bacteria while sparing the commensal microbiota [39]. It was also observed that acidic cervicovaginal mucus (CVM) (acidified to approximately pH 4 by lactic acid produced continuously by anaerobic metabolism of Lactobacilli) trapped human immunodeficiency virus (HIV) while neutral CVM did not [40]. The trapping of HIV particles by mucoadhesion was also shown to be specifically associated with lactic acid [40]. The acidic milieu common to the vaginal vault of the adult female is most commonly attributed to the presence of Lactobacillus acidophilus.

For a long time, acidification of the vaginal vault by Lactobacillus and other acid-producing microbes was believed to be main effector of vaginal immunity. Lactic acid, however, is not produced only by Lactobacilli but also by vaginal mucosa [41], a significant source of lactic acid in the vaginal fluid [17]. There is no correlation between the number of Lactobacilli present and the pH of the vagina, which is not noticeably affected when Lactobacillus is absent in any significant numbers [17]. In addition, the vaginal vault of the newborn female, while sterile, contains substantial lactate and is acidic [42].

In addition, the use of non culture -dependent gene amplification techniques capable of producing molecular identification of component species has revealed that the traditional view of L. acidophilus as the obligatory foundation of an acidic vaginal environment is an oversimplification. Recent molecular studies have demonstrated that other Lactobacillus species, including L. crispatus, L. gasseri, L. iners, L. gallinarum and L vaginalis, are capable of providing a vaginal environment rich in lactic acid as well. In addition, other acid-producing species have been identified in some women lacking a dominance of Lactobacilli, particularly Atopobium, Megasphaera, and Leptotrichia, which are also associated with an acidic vaginal fluid [8,13,14].

Some have suggested that hydrogen peroxide production by Lactobacillus species is the primary effector of acidity in the vagina. Hydrogen peroxide (H2O2) is a broad-spectrum disinfectant and cervicovaginal fluid (CVF) is known to contain myeloperoxidase that enhances pathogen inactivation by H2O2 [43]. Women with vaginal microbiota predominantly colonized with H2O2-producing lactobacilli may be less likely to be infected by a number of nonresident pathogens, including HIV-1, herpes simplex virus-2 (HSV-2), Trichomonas vaginalis, Gardnerella vaginalis, and Gram-negative microorganisms associated with bacterial vaginosis (BV) [43]. In fact, the incidence of BV was observed by multiple authors to be inversely related to colonization by H2O2-producing bacteria [44-47].

Hydrogen peroxide-producing lactobacilli have also been shown to be specifically associated with homeostasis of the vaginal mucosa [37]. Biological concentrations of H2O2 measured in vaginal fluid are toxic to many nonresident microbiota, which suggests these Lactobacilli may be more beneficial to the host than Lactobacilli that do not generate H2O2. However, the above studies were performed using in vitro cultures. A recent study has demonstrated that CVF or semen inactivates H2O2 bringing into question whether it has any physiological role in the female genital tract [43].

Lactobacillus spp. have also been shown to compete for adherence to the vaginal epithelium, thereby interfering with colonization by pathogenic organisms [48]. Finally, Lactobacilli are also known to produce bacteriocins, broad-spectrum antimicrobial peptides [49].

Vaginal secretions

The vaginal fluid, secreted at about 2 mL a day [17], participates in mechanical defense of the mucosal surface as secretions continually wash pathogens toward the vaginal opening. Vaginal secretions also trap potential pathogens [17]. The vaginal fluid contains epithelial cells and stromal cells, as well as immune cells that migrate into the uterus, cervix, and vagina [50]. It is also replete with antibodies. Immunoglobin A (IgA) and IgG are produced by local B cells or transduced into the vaginal fluid from the systemic circulation [20]. Secretory IgA (sIgA) is produced by plasma cells adjacent to submucosal glands [11].

The vaginal fluid also contains mucus as well as fluids from the endometrium, Fallopian tubes, and vestibular glands [51]. Concentrations of vaginal fluid components vary depending on sexual stimulation and the presence or absence of secretory inducers [52]. There are also hormonal influences on vaginal secretions, as estrogen stimulates the glycogen-rich intermediate cell layer of the mucosa which has the greatest metabolic and secretory activity [17], including variations in the numbers of exfoliated cells [52].

There are a wide variety of organic molecules in the vaginal secretions. Lactic acid is a main component, but the vaginal fluid also contains multiple aliphatic acids, alcohols, glycols, and aromatic compounds [53], as well as urea and at least 339 proteins [54], many of which are the products of the innate and adaptive immunity systems in the vaginal environment.

Neutrophils, macrophages, and NK cells contribute numerous defense effector molecules, including cathelicidin, TLKs, calprotection, defnesisns, and SLP1 [11,12,50] Epithelial cells, when confronted by a pathogenic invader, secrete a variety of defense-effector molecules [32]. Cervicovaginal epithelial cells secrete numerous cytokines, chemokines, and other peptides which, with other components of the cervicovaginal milieu, comprise the vaginal fluid. It is now known that the vaginal secretions contain numerous antimicrobial substances, such as defensins, cathelicidin, lactoferrin, lysozyme, calprotectin, elafin, and secretory leukoprotease inhibitor (SLPI), and chemokines secreted from serous cells in submucosal glands [11], whose contributions to cervicovaginal immunity are only recently being understood.

Antimicrobial molecules

These cationic peptides of innate immunity are slowly being recognized as the principal effector molecules of cervicovaginal immunity. Most antimicrobial peptides and proteins are broadspectrum microbicides that target Gram-positive and Gram-negative bacteria as well as fungi and some enveloped viruses by a variety of different mechanisms [55]; there is evidence that these secretory products may help regulate both innate and adaptive immunity by acting as both signal molecules and effectors [32]. Although a plethora of antimicrobial products are produced by the innate immune constituents in the cervical-vaginal tract, they have a tendency to share several chemical properties, including amphipathicity (spatial separation of polar and nonpolar residues), as well as cationicity (maintenance of a positive charge at physiological pH), facilitating insertion into microbial membranes. Thus, they appear to play multiple roles in host defense [11].

Antimicrobial peptides are constitutively expressed by epithelial cells and regulated by various inflammatory mediators and bacterial products [32]. Epithelial cells and granulocytes synthesize additional antimicrobial peptides [56]. Epithelial cells produce functional antimicrobials; granulocytes in early stages of differentiation produce antimicrobials which are packaged into granules, with antimicrobials later released during activation [57]. The primary antimicrobial components of innate immunity are discussed briefly below and elaborated in more detail in table 4.

Effector Molecule Source Activity Target Organisms
Lysozyme 13 µg/mL in vaginal fluid, 1 mg/mL in mucus plug [92] Secreted by serous cells in submucosal glands [11]  Cleaves bonds in peptidoglycan component of cell walls, cationic disruption of microbial membranes [93] Gram-negative bacteria [93]
Weak at normal concentrations against bacteria, some antiviral (HIV) [94]
Lactoferrin
1 µg/mL in vaginal fluid, 100 µg/mL in cervical plug [92]
Secreted by serous cells in submucosal glands [11]* Sequesters iron, also disrupts microbial membranes [11]
Inhibits cellular fusion and entry by virus [95]
Gram negative bacteria [93] , virus [95]
Calprotectin
34 µg/mL [11]
Component of neutrophils, monocytes and keratinocytes [95] Sequesters zinc [11] Inhibits growth of fungi and yeast [96]
Human Alpha Defensins HPN 1,2,3,4 about 2 µg/mL [59] Synthesized in bone marrow [97] Comprise contents of phagocytic vacuoles that effect microbicidal activity [98]
increase the production of TNF and IL-1
Bacteria, fungi, viruses [11]
5 HD5
10 to 40 ng/mL
Columnar epithelium of endocervix [99] Binds electrostatically to negatively charged microbial particle, forming pores in cell membrane and eventually causing lysis [100] Bacteria, fungi, viruses [11]
Human Beta Defensins vaginal epithelial cells leukocytes [11]
HBD‑1 is produced constitutively in mucosa [11]
Human defensins HBD2 and 3 are induced at inflamed sites [11]    
Antimicrobial activity, inhibition of HIV-infectivity of immunocompetent cells, chemoattraction of T cells immature dendritic cells B cells neutrophils and macrophages [101,102] Gram-positive or Gram- negative bacteria, mycobacteria. yeast, enveloped viruses viral (in vitro) [103]
SLPI
10 to 100 µg/mL in vaginal secretions, as high as 1000 µg/mL in cervical mucus plug [11]    
Found in epithelial secretions, also produced by macrophages [11] Blocks action of hostile enzymes released by invading organisms [3]  Suppresses central transcription factor of inflammatory response [104] Bacteria and fungi  (weak at normal concentrations) [11]
 Antiviral (HIV-1) [61]
Surfactin Protein A In vaginal secretions [105, 106] Facilitates phagocytosis of microbes, increases chemotaxis, increases oxidative burst by phagocytes, modulates pro- inflammatory cytokine production by immune cells [105- 107] Bacteria, viruses [105, 106]
Surfactin Protein D In vaginal secretions [108] Increases permeability of bacterial cell membranes [107]
  stimulates oxygen radical release, contributing to destruction of virus [109]
Bacteria [107], viruses [108]
MBL Transudate from liver Facilitates complement activation and opsonization by binding to pathogenic microbes [63]  
Elafin Epithelial cells Antimicrobial , inhibits inflammation-related tissue damage by blocking elastase [3]  
Cathelicidin (LL-37)
1 µg/mL[11]
Components of neutrophils[11] Postcoital processing from hCAP18 precursor to functional form, targeting specifically microbes which may have been introduced by intercourse [110] Bacteria and fungi [11]

HBD= human beta defensin; hCAP-18 = human cationic antimicrobial protein; HD5 = human alpha defensin 5; HIV = human immunodeficiency virus; HPN = human alpha defensin; IL‑1 = Interleukin-1; MBL = mannose binding lectin; SLPI = secretory leukocyte protease inhibitor; TNF = tumor necrosis factor

Table 4: Defense Effector Molecules in Innate Immunity.

Defensins are an important component of innate immunity at the mucosal surface in the lower genital tract. They are small, positively charged peptides that bind to the negatively charged bacterial surface and disrupt bacterial membranes resulting in lysis [58]. Defensins are broad spectrum antimicrobials, with efficacy against both Gramnegative and Gram-positive bacteria, as well as fungi, protozoa. and enveloped viruses and contain six cysteine residues forming three sulfide bridges [1].

Human alpha-defensins (HNP 1-4) are produced by neutrophils [59], while alpha human defensins (HD) HD 5 and 6 are expressed by epithelial cells of the female genital tract [56,59]. Human beta defensins, are produced by various epithelial cells of the female reproductive tract [56,60]; some constitutively, some are induced by microbial components or by pro-inflammatory cytokines [32].

Secretory leukoprotease inhibitor is produced by macrophages and epithelial cells and inhibits proteolytic activity of neutrophil elastase, cathepsin G, trypsin and chymotrypsin and also exhibits antimicrobial activity [32]. High levels of SLPI in vaginal fluid have been associated with reduced rates of perinatal HIV-1 transmission [61]; low levels are associated with the presence of genital tract infections [62].

Mannose binding lectin (MBL) recognizes carbohydrate patterns on the surface of a variety of pathogenic microorganisms, including bacteria, viruses, protozoa and fungi. Binding of MBL to a microorganism results in activation of the complement system as well as opsonization [63].

Elafin is expressed by epithelial cells in the CVM and inhibits activity of neutrophil elastase and proteinase 3 (PRTN3) [32]. Cathelicidins (LL-37) are components of neutrophils, but are also found in various squamous epithelia as well as keratinocytes in inflamed skin (inflammatory mediators implicated as the regulatory of LL-37 expression [64]. A specific cathelicidin LL-37, found in the vaginal fluid, is the end result of processing induced by the act of sexual intercourse and is characterized by a broad spectrum of activity against both bacteria and fungi [11].

Cystatins are inhibitors of microbial cysteine proteases [65]. Cystatins A, C, and S have also been observed to have antimicrobial activity against bacteria and viruses [32].

Calprotectin is a heterodimeric protein component of neutrophils, monocytes and keratinocytes, also known as leukocyte protein L1 and calgranulin. At biological concentrations calprotectin inhibits the growth of fungi and bacteria in vitro by sequestering zinc [11].

Lysozyme cleaves the bonds in peptidoglycan, a molecules ubiquitous in microbial cell walls, allowing it to disrupt microbial membranes. It may act in synergy with other antimicrobial components of epithelia secretions [11].

Lactoferrin is an abundant component of some epithelia as well as neutrophil granules which eliminate microbes directly as well as by sequestration of iron [11].

Virtually all of the secretory products of the innate immune system are considered to be estrogen dependent. Menopause, with its declining levels of estrogen, is characterized by a parallel decline in the levels of secretory products in the vaginal fluid [3].

Discussion

Innate immunity in the female reproductive tract is of much current interest as a fascinating and interconnected array of multifunctional components of immunity are being revealed. The abundance and diversity of antimicrobial factors in the vaginal milieu would suggest a synergistic effect. Products of both host cells as well as the resident microflora, each molecule contributes a highly specific immunological function. As a family of immune effectors, however, together the molecules produce a formidable, barrier. An intact mucosal epithelium, for example, in conjunction with innate immune mechanisms and adaptive immune functions prevents 99% of HIV exposures from producing infection--a success factor far more impressive than any HIV vaccine currently in production [66].

The highly developed innate immune complex in the unique CVM, in addition, permits preservation of immune surveillance and antipathogen functions while maintaining a favorable environment for reproduction.

Epithelial cells, responding to both estrogen and the multiple effect or molecules that are simultaneously stimulated by estrogen, enable bidirectional communication between epithelial cells that effectively regulate both reproductive and immune function in order to maintain the delicate balance between immunity and reproduction, between pathogenic and commensal microorganisms and sperm and the developing fetus [20]. Further understanding of the regulation of expression and activity of the multitude of microbial peptides that make up a significant part of innate immunity in the lower genital tract will facilitate strategies to further improve female reproductive tract health.

References

  1. Quayle AJ (2002) The innate and early immune response to pathogen challenge in the female genital tract and the pivotal role of epithelial cells. J Reprod Immunol 57: 61-79.
  2. Abrahams VM, Mor G (2005) Toll-like receptors and their role in the trophoblast. Placenta 26: 540-547.
  3. Summers P (2010) Unique skin immunology of the lower female genital tract with age. In Textbook of aging skin. Farage MA, Miller KW & Maibach HI (Eds.) 253-256.
  4. Janeway CA, Travers P, Walport M, Shlomchik M (2005) Immunogiology: The Immune System in Health and Disease. Garland Science Publishing, New York.
  5. Packiam M, Veit SJ, Anderson DJ, Ingalls RR, Jerse AE (2010) Mouse straindependent differences in susceptibility to Neisseria gonorrhoeae infection and induction of innate immune responses. Infect Immun 78: 433-440.
  6. Barton PT, Gerber S, Skupski DW, Witkin SS (2003) Interleukin-1 receptor antagonist gene polymorphism, vaginal interleukin-1 receptor antagonist concentrations, and vaginal ureaplasma urealyticum colonization in pregnant women. Infect Immun 71: 271-274.
  7. Genc MR, Vardhana S, Delaney ML, Onderdonk A, Tuomala R, et al. (2004) Relationship between a toll-like receptor-4 gene polymorphism, bacterial vaginosis-related flora and vaginal cytokine responses in pregnant women. Eur J Obstet Gynecol Reprod Biol 116: 152-156.
  8. Zhou X, Brown CJ, Abdo Z, Davis CC, Hansmann MA, et al. (2007) Differences in the composition of vaginal microbial communities found in healthy caucasian and black women. ISME J 1: 121-133.
  9. Wira CR, Grant-Tschudy KS, Crane-Godreau MA (2005) Epithelial cells in the female reproductive tract: a central role as sentinels of immune protection. Am J Reprod Immunol 53: 65-76.
  10. Ravetch JV, Bolland S (2001) IgG Fc receptors. Annu Rev Immunol 19: 275- 290.
  11. Cole AM (2006) Innate host defense of human vaginal and cervical mucosae. Curr Top Microbiol Immunol 306: 199-230.
  12. Nasu K, Narahara H (2010) Pattern recognition via the toll-like receptor system in the human female genital tract. Mediators Inflamm 976024.
  13. Ravel J, Gajer P, Abdo Z, Schneider GM, Koenig SS, et al. (2011) Vaginal microbiome of reproductive-age women. Proc Natl Acad Sci USA 108: 4680- 4687.
  14. Zhou X, Bent SJ, Schneider MG, Davis CC, Islam MR, et al. (2004) Characterization of vaginal microbial communities in adult healthy women using cultivation-independent methods. Microbiology 150: 2565-2573.
  15. Kierszenbaum AL (2002) Histology and cell biology: an introduction to pathology. Mosby St Louis.
  16. Oats J, Abraham S (2004) Llewellyn-jones fundamentals of obstetrics gynaecology . Mosby, Edinburgh New York.
  17. Summers PR (2010) Vaginal secretions with age. In Textbook of aging skin. Farage MA, Miller KW, Maibach HI (Eds.) 247-251.
  18. Lai SK, Wang Y, Wirtz D, Hanes J (2009) Micro- and macrorheology of mucus. Adv Drug Deliv Rev 61: 86-100.
  19. Patton DL, Thwin SS, Meier A, Hooton TM, Stapleton AE, et al. (2000) Epithelial cell layer thickness and immune cell populations in the normal human vagina at different stages of the menstrual cycle. Am J Obstet Gynecol 183: 967-973.
  20. Wira CR, Fahey JV, Ghosh M, Patel MV, Hickey DK, et al. (2010) Sex hormone regulation of innate immunity in the female reproductive tract: the role of epithelial cells in balancing reproductive potential with protection against sexually transmitted pathogens. Am J Reprod Immunol 63: 544-565.
  21. Yuan Q, Walker WA (2004) Innate immunity of the gut: mucosal defense in health and disease. J Pediatr Gastroenterol Nutr 38: 463-473.
  22. Medzhitov R, Janeway CA (1997) Innate immunity: the virtues of a nonclonal system of recognition. Cell 91: 295-298.
  23. Heil F, Hemmi H, Hochrein H, Ampenberger F, Kirschning C, et al. (2004) Species-specific recognition of single-stranded RNA via toll-like receptor 7 and 8. Science 303: 1526-1529.
  24. Andersen JM, Al-Khairy D, Ingalls RR (2006) Innate immunity at the mucosal surface: role of toll-like receptor 3 and toll-like receptor 9 in cervical epithelial cell responses to microbial pathogens. Biol Reprod 74: 824-831.
  25. Pivarcsi A, Nagy I, Koreck A, Kis K, Kenderessy-Szabo A, et al. (2005) Microbial compounds induce the expression of pro-inflammatory cytokines, chemokines and human beta-defensin-2 in vaginal epithelial cells. Microbes Infect 7: 1117- 1127.
  26. Iversen MB, Ank N, Melchjorsen J, Paludan SR (2010) Expression of type III interferon (IFN) in the vaginal mucosa is mediated primarily by dendritic cells and displays stronger dependence on NF-kappaB than type I IFNs. J Virol 84: 4579-4586.
  27. Fichorova RN, Cronin AO, Lien E, Anderson DJ, Ingalls RR (2002) Response to Neisseria gonorrhoeae by cervicovaginal epithelial cells occurs in the absence of toll-like receptor 4-mediated signaling. J Immunol 168: 2424-2432.
  28. Abrahams VM (2005) Toll-like receptors in the cycling female reproductive tract and during pregnancy. Curr Womens Health Rev 1: 35-42.
  29. Lin Z, Xu J, Jin X, Zhang X, Ge F (2009) Modulation of expression of toll-like receptors in the human endometrium. Am J Reprod Immunol 61: 338-345.
  30. Pioli PA, Amiel E, Schaefer TM, Connolly JE, Wira CR, et al. (2004) Differential expression of toll-like receptors 2 and 4 in tissues of the human female reproductive tract. Infect Immun 72: 5799-5806.
  31. Beutler B (2004) Inferences, questions and possibilities in toll-like receptor signalling. Nature 430: 257-263.
  32. Tjabringa GS, Vos JB, Olthuis D, Ninaber DK, Rabe KF, et al. (2005) Host defense effector molecules in mucosal secretions. FEMS Immunol Med Microbiol 45: 151-158.
  33. Costerton W, Veeh R, Shirtliff M, Pasmore M, Post C, et al. (2003) The application of biofilm science to the study and control of chronic bacterial infections. J Clin Invest 112: 1466-1477.
  34. Cone RA (2009) Barrier properties of mucus. Adv Drug Deliv Rev 61: 75-85.
  35. Lai SK, Wang Y, Hida K, Cone R, Hanes J (2010) Nanoparticles reveal that human cervicovaginal mucus is riddled with pores larger than viruses. Proc Natl Acad Sci USA 107: 598-603.
  36. Andersch-Björkman Y, Thomsson KA, Holmén Larsson JM, Ekerhovd E, Hansson GC (2007) Large scale identification of proteins, mucins, and their O-glycosylation in the endocervical mucus during the menstrual cycle. Mol Cell Proteomics 6: 708-716.
  37. Hillier SL (1999) Normal vaginal flora. In Sexually transmitted diseases. Holmes KK, Sparling PF, Mardh P, Lemon SM, Stamm WE, Piot P, Wasserheit JN (Eds.) 191-204.
  38. Boskey ER, Cone RA, Whaley KJ, Moench TR (2001) Origins of vaginal acidity: high D/L lactate ratio is consistent with bacteria being the primary source. Hum Reprod 16: 1809-1813.
  39. Valore EV, Park CH, Igreti SL, Ganz T (2002) Antimicrobial components of vaginal fluid. Am J Obstet Gynecol 187: 561-568.
  40. Lai SK, Hida K, Shukair S, Wang YY, Figueiredo A, et al. (2009) Human immunodeficiency virus type 1 is trapped by acidic but not by neutralized human cervicovaginal mucus. J Virol 83: 11196-11200.
  41. Gross M (1961) Biochemical changes in the reproductive cycle. Fertil Steril 12: 245-262.
  42. Raskoff AE, Feo LG, Goldstein L (1943) The biologic characteristics of the normal vagina. Am J Obstet Gynecol 47: 467-494.
  43. O'Hanlon DE, Lanier BR, Moench TR, Cone RA (2010) Cervicovaginal fluid and semen block the microbicidal activity of hydrogen peroxide produced by vaginal lactobacilli. BMC Infect Dis 10: 120.
  44. Eschenbach DA, Davick PR, Williams BL, Klebanoff SJ, Young-Smith K, et al. (1989) Prevalence of hydrogen peroxide-producing lactobacillus species in normal women and women with bacterial vaginosis. J Clin Microbiol 27: 251- 256.
  45. Al-Mushrif S, Jones BM (1998) A study of the prevalence of hydrogen peroxide generating Lactobacilli in bacterial vaginosis: the determination of H2O2 concentrations generated, in vitro, by isolated strains and the levels found in vaginal secretions of women with and without infection. J Obstet Gynaecol 18: 63-67.
  46. Mijac VD, Dukic SV, Opavski NZ, Dukic MK, Ranin LT (2006) Hydrogen peroxide producing lactobacilli in women with vaginal infections. Eur J Obstet Gynecol Reprod Biol 129: 69-76.
  47. Cherpes TL, Hillier SL, Meyn LA, Busch JL, Krohn MA (2008) A delicate balance: risk factors for acquisition of bacterial vaginosis include sexual activity, absence of hydrogen peroxide-producing lactobacilli, black race, and positive herpes simplex virus type 2 serology. Sex Transm Dis 35: 78-83.
  48. Osset J, Bartolomé RM, García E, Andreu A (2001) Assessment of the capacity of lactobacillus to inhibit the growth of uropathogens and block their adhesion to vaginal epithelial cells. J Infect Dis 183: 485-491.
  49. Aroutcheva A, Gariti D, Simon M, Shott S, Faro J, et al. (2001) Defense factors of vaginal lactobacilli. Am J Obstet Gynecol 185: 375-379.
  50. Wira CR, Fahey JV, Sentman CL, Pioli PA, Shen L (2005) Innate and adaptive immunity in female genital tract: cellular responses and interactions. Immunol Rev 206: 306-335.
  51. Paavonen J (1983) Physiology and ecology of the vagina. Scand J Infect Dis Suppl 40: 31-35.
  52. Huggins GR, Preti G (1981) Vaginal odors and secretions. Clin Obstet Gynecol 24: 355-377.
  53. Huggins GR, Preti G (1976) Volatile constituents of human vaginal secretions. Am J Obstet Gynecol 126: 129-136.
  54. Zegels G, Van Raemdonck GA, Coen EP, Tjalma WA, Van Ostade XW (2009) Comprehensive proteomic analysis of human cervical-vaginal fluid using colposcopy samples. Proteome Sci 7: 17.
  55. Ganz T (2003) Defensins: antimicrobial peptides of innate immunity. Nat Rev Immunol 3: 710-720.
  56. Nagaoka I, Hirata M, Sugimoto K, Tsutsumi-Ishii Y, Someya A, et al. (1998) Evaluation of the expression of human CAP18 gene during neutrophil maturation in the bone marrow. J Leukoc Biol 64: 845-852.
  57. Hancock RE (2001) Cationic peptides: effectors in innate immunity and novel antimicrobials. Lancet Infect Dis 1: 156-164.
  58. Doss M, White MR, Tecle T, Hartshorn KL (2010) Human defensins and ll-37 in mucosal immunity. J Leukoc Biol 87: 79-92.
  59. Horne AW, Stock SJ, King AE (2008) Innate immunity and disorders of the female reproductive tract. Reproduction 135: 739-749.
  60. Pillay K, Coutsoudis A, Agadzi-Naqvi AK, Kuhn L, Coovadia HM, et al. (2001) Secretory leukocyte protease inhibitor in vaginal fluids and perinatal human immunodeficiency virus type 1 transmission. J Infect Dis 183: 653-656.
  61. Novak RM, Donoval BA, Graham PJ, Boksa LA, Spear G, et al. (2007) Cervicovaginal levels of lactoferrin, secretory leukocyte protease inhibitor, and RANTES and the effects of coexisting vaginoses in human immunodeficiency virus (HIV)-seronegative women with a high risk of heterosexual acquisition of HIV infection. Clin Vaccine Immunol 14: 1102-1107.
  62. Fraser IP, Koziel H, Ezekowitz RA (1998) The serum mannose-binding protein and the macrophage mannose receptor are pattern recognition molecules that link innate and adaptive immunity. Semin Immunol 10: 363-372.
  63. Zanetti M (2004) Cathelicidins, multifunctional peptides of the innate immunity. J Leukoc Biol 75: 39-48.
  64. Björck L (1990) Proteinase inhibition, immunoglobulin-binding proteins and a novel antimicrobial principle. Mol Microbiol 4: 1439-1442.
  65. Kaul R, Pettengell C, Sheth PM, Sunderji S, Biringer A, et al. (2008) The genital tract immune milieu: an important determinant of HIV susceptibility and secondary transmission. J Reprod Immunol 77: 32-40.
  66. Nardelli-Haefliger D, Wirthner D, Schiller JT, Lowy DR, Hildesheim A, et al. (2003) Specific antibody levels at the cervix during the menstrual cycle of women vaccinated with human papillomavirus 16 virus-like particles. J Natl Cancer Inst 95: 1128-1137.
  67. Kilian M, Mestecky J, Russell MW (1988) Defense mechanisms involving Fcdependent functions of immunoglobulin A and their subversion by bacterial immunoglobulin A proteases. Microbiol Rev 52: 296-303.
  68. Abraham SN, Beachey EH (1985) Host defenses against adhesion of bacteria to mucosal surfaces, volume 4. In Advances in host defense mechansisms. Gallin JF, Fauci AS (Eds.) 63-68.
  69. Magnusson KE, Stendahl O, Stjernström I, Edebo L (1979) Reduction of phagocytosis, surface hydrophobicity and charge of Salmonella typhimurium 395 MR10 by reaction with secretory IgA (SIgA). Immunology 36: 439-447.
  70. Svanborg Edén C, Andersson B, Hagberg L, Hanson LA, Leffler H, et al. (1983) Receptor analogues and anti-pili antibodies as inhibitors of bacterial attachment in vivo and in vitro. Ann N Y Acad Sci 409: 580-592.
  71. Russell-Jones GJ, Ey PL, Reynolds BL (1981) Inhibition of cutaneous anaphylaxis and arthus reactions in the mouse by antigen-specific IgA. Int Arch Allergy Appl Immunol 66: 316-325.
  72. Mansa B, Kilian M (1986) Retained antigen-binding activity of Fab alpha fragments of human monoclonal immunoglobulin A1 (IgA1) cleaved by IgA1 protease. Infect Immun 52: 171-174.
  73. Lowell GH, Smith LF, Griffiss JM, Brandt BL, MacDermott RP (1980) Antibodydependent mononuclear cell-mediated antimeningococcal activity. Comparison of the effects of convalescent and postimmunization immunoglobulins G, M, and A. J Clin Invest 66: 260-267.
  74. Tagliabue A, Boraschi D, Villa L, Keren DF, Lowell GH, et al. (1984) IgAdependent cell-mediated activity against enteropathogenic bacteria: distribution, specificity, and characterization of the effector cells. J Immunol 133: 988-992.
  75. Arnold RR, Russell JE, Devine SM, Adamson M, Pruit KM (1984) Antimicrobial activity of the secretory innate defense factors lactoferrin, lactoperoxidase, and lysozyme. In Cariology today. Guggenheim B (Ed.) 75-88.
  76. Magnusson KE, Stjernström I (1982) Mucosal barrier mechanisms. interplay between secretory IgA (SIgA), IgG and mucins on the surface properties and association of salmonellae with intestine and granulocytes. Immunology 45: 239-248.
  77. Hocini H, Barra A, Bélec L, Iscaki S, Preud'homme JL, et al. (1995) Systemic and secretory humoral immunity in the normal human vaginal tract. Scand J Immunol 42: 269-274.
  78. Kozlowski PA, Cu-Uvin S, Neutra MR, Flanigan TP (1997) Comparison of the oral, rectal, and vaginal immunization routes for induction of antibodies in rectal and genital tract secretions of women. Infect Immun 65: 1387-1394.
  79. Belec L, Tevi-Benissan C, Pillot J (1994) Cervico-vaginal synthesis of secretory-IgA and IgG to HIV associated with transudation of serum-borne IgG to HIV, expressing differential avidity to gp160, in HIV-1-infected women. Int Conf AIDS 10: 82.
  80. Eriksson K, Quiding-Järbrink M, Osek J, Möller A, Björk S, et al. (1998) Specificantibody- secreting cells in the rectums and genital tracts of nonhuman primates following vaccination. Infect Immun 66: 5889-5896.
  81. Pudney J, Quayle AJ, Anderson DJ (2005) Immunological microenvironments in the human vagina and cervix: mediators of cellular immunity are concentrated in the cervical transformation zone. Biol Reprod 73: 1253-1263.
  82. Vivier E, Raulet DH, Moretta A, Caligiuri MA, Zitvogel L, et al. (2011) Innate or adaptive immunity? the example of natural killer cells. Science 331: 44-49.
  83. Takeuchi O, Hoshino K, Kawai T, Sanjo H, Takada H, et al. (1999) Differential roles of TLR2 and TLR4 in recognition of gram-negative and gram-positive bacterial cell wall components. Immunity 11: 443-451.
  84. Lien E, Sellati TJ, Yoshimura A, Flo TH, Rawadi G, et al. (1999) Toll-like receptor 2 functions as a pattern recognition receptor for diverse bacterial products. J Biol Chem 274: 33419-33425.
  85. Kirschning CJ, Schumann RR (2002) TLR2: cellular sensor for microbial and endogenous molecular patterns. Curr Top Microbiol Immunol 270: 121-144.
  86. Alexopoulou L, Holt AC, Medzhitov R, Flavell RA (2001) Recognition of doublestranded rna and activation of NF-kappaB by Toll-like receptor 3. Nature 413: 732-738.
  87. Hayashi F, Smith KD, Ozinsky A, Hawn TR, Yi EC, et al. (2001) The innate immune response to bacterial flagellin is mediated by Toll-like receptor 5. Nature 410: 1099-1103.
  88. Diebold SS, Kaisho T, Hemmi H, Akira S, Reis e Sousa C (2004) Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA. Science 303: 1529-1531.
  89. Hemmi H, Takeuchi O, Kawai T, Kaisho T, Sato S, et al. (2000) A toll-like receptor recognizes bacterial DNA. Nature 408: 740-745.
  90. Aflatoonian R, Tuckerman E, Elliott SL, Bruce C, Aflatoonian A, et al. (2007) Menstrual cycle-dependent changes of Toll-like receptors in endometrium. Hum Reprod 22: 586-593.
  91. Hein M, Valore EV, Helmig RB, Uldbjerg N, Ganz T (2002) Antimicrobial factors in the cervical mucus plug. Am J Obstet Gynecol 187: 137-144.
  92. Ellison RT, Giehl TJ (1991) Killing of gram-negative bacteria by lactoferrin and lysozyme. J Clin Invest 88: 1080-1091.
  93. Lee-Huang S, Maiorov V, Huang PL, Ng A, Lee HC, et al. (2005) Structural and functional modeling of human lysozyme reveals a unique nonapeptide, HL9, with anti-HIV activity. Biochemistry 44: 4648-4655.
  94. Swart PJ, Kuipers EM, Smit C, Van Der Strate BW, Harmsen MC, et al. (1998) Lactoferrin. Antiviral activity of lactoferrin. Adv Exp Med Biol 443: 205-213.
  95. Steinbakk M, Naess-Andresen CF, Lingaas E, Dale I, Brandtzaeg P, et al. (1990) Antimicrobial actions of calcium binding leucocyte L1 protein, calprotectin. Lancet 336: 763-765.
  96. Valore EV, Ganz T (1992) Posttranslational processing of defensins in immature human myeloid cells. Blood 79: 1538-1544.
  97. Ganz T, Selsted ME, Szklarek D, Harwig SS, Daher K, et al. (1985) Defensins. Natural peptide antibiotics of human neutrophils. J Clin Invest 76: 1427-1435.
  98. Quayle AJ, Porter EM, Nussbaum AA, Wang YM, Brabec C, et al. (1998) Gene expression, immunolocalization, and secretion of human defensin-5 in human female reproductive tract. Am J Pathol 152: 1247-1258.
  99. Zasloff M (2002) Antimicrobial peptides of multicellular organisms. Nature 415: 89-395.
  100. Ghosh SK, Gerken TA, Schneider KM, Feng Z, McCormick TS, et al. (2007) Quantification of human beta-defensin-2 and -3 in body fluids: application for studies of innate immunity. Clin Chem 53: 757-765.
  101. Singh PK, Tack BF, McCray PB, Welsh MJ (2000) Synergistic and additive killing by antimicrobial factors found in human airway surface liquid. Am J Physiol Lung Cell Mol Physiol 279: 799-805.
  102. Quiñones-Mateu ME, Lederman MM, Feng Z, Chakraborty B, Weber J, et al. (2003) Human epithelial beta-defensins 2 and 3 inhibit HIV-1 replication. AIDS 17: 39-48.
  103. Taggart CC, Cryan S, Weldon S, Gibbons A, Greene CM, et al. (2005) Secretory leucoprotease inhibitor binds to NF-kappaB binding sites in monocytes and inhibits p65 binding. J Exp Med 202: 1659-1668.
  104. MacNeill C, Umstead TM, Phelps DS, Lin Z, Floros J, et al. (2004) Surfactant protein A, an innate immune factor, is expressed in the vaginal mucosa and is present in vaginal lavage fluid. Immunology 111: 91-99.
  105. Meschi J, Crouch EC, Skolnik P, Yahya K, Holmskov U, et al. (2005) Surfactant protein D binds to human immunodeficiency virus (HIV) envelope protein gp120 and inhibits HIV replication. J Gen Virol 86: 3097-3107.
  106. Wu H, Kuzmenko A, Wan S, Schaffer L, Weiss A, et al. (2003) Surfactant proteins A and D inhibit the growth of Gram-negative bacteria by increasing membrane permeability. J Clin Invest 111: 1589-1602.
  107. John M, Keller MJ, Fam EH, Cheshenko N, Hogarty K, et al. (2005) Cervicovaginal secretions contribute to innate resistance to herpes simplex virus infection. J Infect Dis 192: 1731-1740.
  108. LeVine AM, Gwozdz J, Stark J, Bruno M, Whitsett J, et al. (1999) Surfactant protein-A enhances respiratory syncytial virus clearance in vivo. J Clin Invest 103: 1015-1021.
  109. Sørensen OE, Gram L, Johnsen AH, Andersson E, Bangsbøll S, et al. (2003) Processing of seminal plasma hCAP-18 to ALL-38 by gastricsin: a novel mechanism of generating antimicrobial peptides in vagina. J Biol Chem 278: 28540-28546.
Citation: Farage MA, Miller KW, Gerberick GF, Saito FH, Ledger WJ, et al. (2011) Innate Immunity in the Lower Female Mucosal Tract. J Steroids Hormon Sci 2:106.

Copyright: © 2011 Farage MA, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.