Role for dendritic cells in immunoregulation during experimental vaginal candidiasis

Immunopathology of COVID-19 and its implications in the development of rhino-orbital-cerebral mucormycosis: a major review

PURPOSE

To present a literature review on various immunopathologic dysfunctions following COVID-19 infection and their potential implications in development of rhino-orbital-cerebral mucormycosis (ROCM).

METHODS

A literature search was performed via Google Scholar and PubMed with subsequent review of the accompanying references. Analogies were drawn between the immune and physiologic deviations caused by COVID-19 and the tendency of the same to predispose to ROCM.

RESULTS

Sixty-two articles were reviewed. SARS-CoV-2 virus infection leads to disruption of epithelial integrity in the respiratory passages, which may be a potential entry point for the ubiquitous Mucorales to become invasive. COVID-19 related GRP78 protein upregulation may aid in spore germination and hyphal invasion by Mucorales. COVID-19 causes interference in macrophage functioning by direct infection, a tendency for hyperglycemia, and creation of neutrophil extracellular traps. This affects innate immunity against Mucorales. Thrombocytopenia and reduction in the number of natural killer (NK) cells and infected dendritic cells is seen in COVID-19. This reduces the host immune response to pathogenic invasion by Mucorales. Cytokines released in COVID-19 cause mitochondrial dysfunction and accumulation of reactive oxygen species, which cause oxidative damage to the leucocytes. Hyperferritinemia also occurs in COVID-19 resulting in suppression of the hematopoietic proliferation of B- and T-lymphocytes.

CONCLUSIONS

COVID-19 has a role in the occurrence of ROCM due to its effects at the entry point of the fungus in the respiratory mucosa, effects of the innate immune system, creation of an environment of iron overload, propagation of hyperglycemia, and effects on the adaptive immune system.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

The Role of T Helper 17 (Th17) and Regulatory T Cells (Treg) in the Pathogenesis of Vulvovaginal Candidiasis among HIV-Infected Women

Background. The study sought to describe relationships between 20 cytokines and chemokines (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-17, G-CSF, GM-CSF, IFN-γ, MCP-1, MIP-1β, TNF-α, TGF-β1, TGF-β2, and TGF-β3) and the presence of vulvovaginal candidiasis (VVC) in women, stratified by HIV status. Methods. Plasma and genital samples were obtained from 51 clinic attendees in KwaZulu-Natal between June 2011 and December 2011. Cytokine and chemokine concentrations were measured by Luminex® multiplex immunoassays. Multiple comparisons of means of cytokine/chemokine levels displaying significant differences in univariate analyses across the study groups were performed using post hoc Bonferroni pairwise tests considering a type I error rate of 0.05. A discriminant analysis (DA) was carried out to identify linear combinations of variates that would maximally discriminate group memberships. Results. Of the 51 participants, 16/26 HIV-infected and 15/25 HIV-uninfected women were diagnosed with VVC. DA identified 2 variables (MIP-1β and TGF-β3) in plasma (Box’s M (5.49), $p$ (0.57) > α (0.001); Wilks’ lambda = 0.116, $p<0.0001$ ) and 1 variable (IL-13) in vaginal secretions (Box’s M (2.063), $p$ (0.37) > α (0.001); Wilks’ lambda = .677, $p<0.0001$ ) as able to discriminate the HIV + VVC + group, whilst TGF-β1 in plasma discriminated the HIV + VVC − group. Mean concentrations of genital IL-6, IL-8, IL-10, IL-17, and TGF-β3 were significantly higher in HIV infected women coinfected with VVC. Conclusions. In HIV-infected women, VVC might be explained by a decline of Th17 cells, hence a decrease of Th17/Treg ratio.

Applying the Host-Microbe Damage Response Framework to Candida Pathogenesis: Current and Prospective Strategies to Reduce Damage

Disease is a complex outcome that can occur as a result of pathogen-mediated damage, host-mediated damage or both. This has led to the revolutionary concept of the damage response framework (DRF) that defines microbial virulence as a function of host immunity. The DRF outlines six scenarios (classes) of host damage or beneficial outcomes, depending on the microbe and the strength of the immune response. Candida albicans is uniquely adapted to its human host and can exist as either a commensal, colonizing various anatomical sites without causing notable damage, or as a pathogen, with the ability to cause a diverse array of diseases, ranging from mucosal to invasive systemic infections that result in varying levels of microbe-mediated and/or host-mediated damage. We recently categorized six different forms of candidiasis (oropharyngeal, hematogenous, intra-abdominal, gastrointestinal, denture stomatitis, and vulvovaginitis) into independent DRF classes, supporting a contemporary view of unique mechanisms of pathogenesis for these Candida infections. In this review, we summarize the evidence for the pathogenesis of these various forms of candidiasis in the context of the DRF with the further intent to provide insights into strategies to achieve a level of host response or outcome otherwise, that limits host damage.

Immunopathology of Recurrent Vulvovaginal Infections: New Aspects and Research Directions

Recurrent vulvovaginal infections (RVVI), a devastating group of mucosal infection, are severely affecting women's quality of life. Our understanding of the vaginal defense mechanisms have broadened recently with studies uncovering the inflammatory nature of bacterial vaginosis, inflammatory responses against novel virulence factors, innate Type 17 cells/IL-17 axis, neutrophils mediated killing of pathogens by a novel mechanism, and oxidative stress during vaginal infections. However, the pathogens have fine mechanisms to subvert or manipulate the host immune responses, hijack them and use them for their own advantage. The odds of hijacking increases, due to impaired immune responses, the net magnitude of which is the result of numerous genetic variations, present in multiple host genes, detailed in this review. Thus, by underlining the role of the host immune responses in disease etiology, modern research has clarified a major hypothesis shift in the pathophilosophy of RVVI. This knowledge can further be used to develop efficient immune-based diagnosis and treatment strategies for this enigmatic disease conditions. As for instance, plasma-derived MBL replacement, adoptive T-cell, and antibody-based therapies have been reported to be safe and efficacious in infectious diseases. Therefore, these emerging immune-therapies could possibly be the future therapeutic options for RVVI.

A review of antioxidant and pharmacological properties of phenolic compounds in Acacia confusa

In the present review article, the phytochemical, antioxidant and pharmacological studies are congregated and summarized concerning the current knowledge of the phenolic compounds of a traditional medical plant Acacia confusa in Taiwan. This plant is native to Taiwan and South-East Asia. It possesses major pharmacological activities, including antioxidant and radical scavenging activity, hepatoprotective effect, xanthine oxidase inhibition, semicarbazide-sensitive amine oxidase inhibition, angiotensin I converting enzyme inhibition, antihyperuricemic effect and anti-inflammatory activity. Phenolic compounds, especially flavonoids, flavonol glycoside and phenolic acid derivatives, are the main phytochemical compounds isolated from different plant parts of A. confusa. Recent interest in this species has focused on pharmacological investigations of the phytochemicals which exhibit potent antioxidant activity based on the multiple phenolic functionalities. The consequence of this review will further extend the potential applications of this plant and offer persuasive support to its future use in the fields of clinical medicine and health functional food.

Innate and Adaptive Immunity to Mucorales

Mucormycosis is an invasive fungal infection characterised by rapid filamentous growth, which leads to angioinvasion, thrombosis, and tissue necrosis. The high mortality rates (50-100%) associated with mucormycosis are reflective of not only the aggressive nature of the infection and the poor therapeutics currently employed, but also the failure of the human immune system to successfully clear the infection. Immune effector interaction with Mucorales is influenced by the developmental stage of the mucormycete spore. In a healthy immune environment, resting spores are resistant to phagocytic killing. Contrarily, swollen spores and hyphae are susceptible to damage and degradation by macrophages and neutrophils. Under the effects of immune suppression, the recruitment and efficacy of macrophage and neutrophil activity against mucormycetes is considerably reduced. Following penetration of the endothelial lining, Mucorales encounter platelets. Platelets adhere to both mucormycete spores and hyphae, and exhibit germination suppression and hyphal damage capacity in vitro. Dendritic cells are activated in response to Mucorales hyphae only, and induce adaptive immunity. It is crucial to further knowledge regarding our immune system's failure to eradicate resting spores under intact immunity and inhibit fungal growth under immunocompromised conditions, in order to understand mucormycosis pathogenicity and enhance therapeutic strategies for mucormycosis.

Recurrent Vulvovaginal Candidiasis: Could It Be Related to Cell-Mediated Immunity Defect in Response to Candida Antigen?

Background

Recurrent vulvovaginal candidiasis (RVVC) is a common cause of morbidity affecting millions of women worldwide. Patients with RVVC are thought to have an underlying immunologic defect. This study has been established to evaluate cell-mediated immunity defect in response to candida antigen in RVVC cases.

Materials and Methods

Our cross-sectional study was performed in 3 groups of RVVC patients (cases), healthy individuals (control I) and known cases of chronic mucocutaneous candidiasis (CMC) (control II). Patients who met the inclusion criteria of RVVC were selected consecutively and were allocated in the case group. Peripheral blood mononuclear cells were isolated and labeled with CFSE and proliferation rate was measured in exposure to candida antigen via flow cytometry.

Results

T lymphocyte proliferation in response to candida was significantly lower in RVVC cases (n=24) and CMC patients (n=7) compared to healthy individuals (n=20, P<0.001), but no statistically significant difference was seen between cases and control II group (P>0.05). Family history of primary immunodeficiency diseases (PID) differed significantly among groups (P=0.01), RVVC patients has family history of PID more than control I (29.2 vs. 0%, P=0.008) but not statistically different from CMC patients (29.2 vs. 42.9%, P>0.05). Prevalence of atopy was greater in RVVC cases compared to healthy individuals (41.3 vs. 15%, P=0.054). Lymphoproliferative activity and vaginal symptoms were significantly different among RVVC cases with and without allergy (P=0.01, P=0.02).

Conclusion

Our findings revealed that T cells do not actively proliferate in response to Candida antigen in some RVVC cases. So it is concluded that patients with cell-mediated immunity defect are more susceptible to recurrent fungal infections of vulva and vagina. Nonetheless, some other cases of RVVC showed normal function of T cells. Further evaluations showed that these patients suffer from atopy. It is hypothesized that higher frequency of VVC in patients with history of atopy might be due to allergic response in mucocutaneous membranes rather than a functional impairment in immune system components.

Slight Pro-Inflammatory Immunomodulation Properties of Dendritic Cells by Gardnerella vaginalis: The "Invisible Man" of Bacterial Vaginosis?

Bacterial vaginosis (BV), the most common genital infection in reproductive-aged women, is associated with increased risk of sexually transmitted infections. Its etiology remains unclear, especially the role of Gardnerella (G.) vaginalis, an anaerobic bacterium characteristic of the BV-alteration of the vaginal ecosystem. In the genital mucosa, dendritic cells (DCs) sense bacteria of the microenvironment via receptors and then orchestrate the immune response by induction of different T cell subtypes. We investigated the interactions between G. vaginalis and human monocyte-derived DCs using a wide range of bacterial concentrations (multiplicity of infection from 0.01 to 100), and the effects of this pathogen on PHA-induced lymphocyte proliferation. As observed by electron microscopy and cytometry, G. vaginalis reduced the internalization ability of DCs by forming extracellular clusters and induced neither DC maturation, nor DC secretion of cytokines, except at the highest dose with a very early DC maturation state. The same profile was observed on lymphocytes with significant increases of proliferation and cytokine secretion only at the highest bacterial concentration. Our findings indicate that G. vaginalis possesses slight immune-stimulating activities against DCs and T cells, reflecting thus a defective inflammatory response and giving rise to the atypical, non- or low-grade, inflammatory clinical disease profile.

Sex Hormones Coordinate Neutrophil Immunity in the Vagina by Controlling Chemokine Gradients

Estradiol-based contraceptives and hormonal replacement therapy predispose women to Candida albicans infections. Moreover, during the ovulatory phase (high estradiol), neutrophil numbers decrease in the vaginal lumen and increase during the luteal phase (high progesterone). Vaginal secretions contain chemokines that drive neutrophil migration into the lumen. However, their expression during the ovarian cycle or in response to hormonal treatments are controversial and their role in vaginal defense remains unknown.To investigate the transepithelial migration of neutrophils, we used adoptive transfer of Cxcr2(-/-) neutrophils and chemokine immunofluorescence quantitative analysis in response to C. albicans vaginal infection in the presence of hormones.Our data show that the Cxcl1/Cxcr2 axis drives neutrophil transepithelial migration into the vagina. Progesterone promotes the Cxcl1 gradient to favor neutrophil migration. Estradiol disrupts the Cxcl1 gradient and favors neutrophil arrest in the vaginal stroma; as a result, the vagina becomes more vulnerable to pathogens.

Adaptive immune responses to Candida albicans infection

Fungal infections are becoming increasingly prevalent in the human population and contribute to morbidity and mortality in healthy and immunocompromised individuals respectively. Candida albicans is the most commonly encountered fungal pathogen of humans, and is frequently found on the mucosal surfaces of the body. Host defense against C. albicans is dependent upon a finely tuned implementation of innate and adaptive immune responses, enabling the host to neutralise the invading fungus. Central to this protection are the adaptive Th1 and Th17 cellular responses, which are considered paramount to successful immune defense against C. albicans infections, and enable tissue homeostasis to be maintained in the presence of colonising fungi. This review will highlight the recent advances in our understanding of adaptive immunity to Candida albicans infections.

Vaginal epithelial cell-derived S100 alarmins induced by Candida albicans via pattern recognition receptor interactions are sufficient but not necessary for the acute neutrophil response during experimental vaginal candidiasis

Vulvovaginal candidiasis (VVC), caused by Candida albicans, affects women worldwide. Animal and clinical studies suggest that the immunopathogenic inflammatory condition of VVC is initiated by S100 alarmins in response to C. albicans, which stimulate polymorphonuclear neutrophil (PMN) migration to the vagina. The purpose of this study was to extend previous in vitro data and determine the requirement for the alarmin S100A8 in the PMN response and to evaluate pattern recognition receptors (PRRs) that initiate the response. For the former, PMN migration was evaluated in vitro or in vivo in the presence or absence of S100 alarmins initiated by several approaches. For the latter, vaginal epithelial cells were evaluated for PRR expression and C. albicans-induced S100A8 and S100A9 mRNAs, followed by evaluation of the PMN response in inoculated PRR-deficient mice. Results revealed that, consistent with previously reported in vitro data, eukaryote-derived S100A8, but not prokaryote-derived recombinant S100A8, induced significant PMN chemotaxis in vivo. Conversely, a lack of biologically active S100A8 alarmin, achieved by antibody neutralization or by using S100A9(-/-) mice, had no effect on the PMN response in vivo. In PRR analyses, whereas Toll-like receptor 4 (TLR4)- and SIGNR1-deficient vaginal epithelial cells showed a dramatic reduction in C. albicans-induced S100A8/S100A9 mRNAs in vitro, inoculated mice deficient in these PRRs showed PMN migration similar to that in wild-type controls. These results suggest that S100A8 alarmin is sufficient, but not necessary, to induce PMN migration during VVC and that the vaginal PMN response to C. albicans involves PRRs in addition to SIGNR1 and TLR4, or other induction pathways.

Female sex hormones regulate the Th17 immune response to sperm and Candida albicans

STUDY QUESTION

What role do female sex hormones play in the antisperm immune response?

SUMMARY ANSWER

We found that sperm induce a Th17 immune response and that estradiol down-regulates the antisperm Th17 response by dendritic cells.

WHAT IS KNOWN ALREADY

Estradiol down-regulates the immune response to several pathogens and impairs the triggering of dendritic cell maturation by microbial products.

STUDY DESIGN, SIZE, DURATION

Ex vivo and in vivo murine models of vaginal infection with sperm and Candida albicans were used to study the induction of Th17 and its hormonal regulation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We analyzed the induction of Th17 cytokines and T cells in splenocytes obtained from BALB/c mice challenged with sperm and C. albicans. For the in vivo vaginal infection models, we used ovariectomized mice treated with vehicle, estradiol or progesterone, and we assessed the effect of these hormones on the immune response in the lymph nodes.

MAIN RESULTS AND THE ROLE OF CHANCE

Th17 cytokines and T cells were induced by sperm antigens in both ex vivo and in vivo experiments. Estrus levels of estradiol down-regulated the Th17 response to sperm and C. albicans in vivo.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted using murine models; whether or not the results are applicable to humans is not known.

WIDER IMPLICATIONS OF THE FINDINGS

Our results describe an adaptive mechanism that reconciles immunity and reproduction and further explains why unregulated Th17 could be linked to infertility and recurrent infections.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by research grants from the Instituto de Salud Carlos III (ISCIII) (PI10/00897) and Fundación Mutua Madrileña to M.R. M.R. holds a Miguel Servet contract from the ISCIII (CP08/00228). M.A.M.-F. was supported by (ISCIII) INTRASALUD PI09/02029. We have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

Not required.

Estradiol downregulates NF-κb translocation by Ikbkg transcriptional repression in dendritic cells

To reconcile immunity and reproduction, females must allow spermatozoa to survive and control the presence of commensal microbiota and sexually transmitted pathogens during ovulation. Female steroid sex hormones exert a powerful effect on the immune system, as do the hormonal changes associated with the ovarian cycle. Dendritic cells (DCs) are immunological sentinels that link innate immunity to adaptive immunity. Upon exposure to microbial invaders in tissue, they undergo a maturational process that culminates in the lymph nodes and activates T-cell-specific immune responses. Estradiol, which is highly expressed during ovulation, has an effect on the maturation of DCs, although the molecular mechanism remains elusive. We detected that estradiol regulates expression of Ikbkg in DCs and modulates nuclear factor-κb translocation to the nucleus, thus explaining the reduced DC function observed during ovulation. This change may be an adaptive mechanism to reconcile control of infection and reproductive functions.

IL-22 and IDO1 affect immunity and tolerance to murine and human vaginal candidiasis

The ability to tolerate Candida albicans, a human commensal of the gastrointestinal tract and vagina, implicates that host defense mechanisms of resistance and tolerance cooperate to limit fungal burden and inflammation at the different body sites. We evaluated resistance and tolerance to the fungus in experimental and human vulvovaginal candidiasis (VVC) as well as in recurrent VVC (RVVC). Resistance and tolerance mechanisms were both activated in murine VVC, involving IL-22 and IL-10-producing regulatory T cells, respectively, with a major contribution by the enzyme indoleamine 2,3-dioxygenase 1 (IDO1). IDO1 was responsible for the production of tolerogenic kynurenines, such that replacement therapy with kynurenines restored immunoprotection to VVC. In humans, two functional genetic variants in IL22 and IDO1 genes were found to be associated with heightened resistance to RVVC, and they correlated with increased local expression of IL-22, IDO1 and kynurenines. Thus, IL-22 and IDO1 are crucial in balancing resistance with tolerance to Candida, their deficiencies are risk factors for RVVC, and targeting tolerance via therapeutic kynurenines may benefit patients with RVVC.

The role of dendritic cells in the innate recognition of pathogenic fungi (A. fumigatus, C. neoformans and C. albicans)

Dendritic cells (DCs) are the bridge between the innate and adaptive immune system. DCs are responsible for sensing and patrolling the environment, initiating a host response and instructing the proper adaptive immune response against pathogens. Recent advances in medical treatments have led to increased use of immunosuppressive drugs, leading to the emergence of fungal species that cause life-threatening infections in humans. Three of these opportunistic fungal pathogens: Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans pose the biggest concern for the immune-compromised host. Here we will review the interactions between DCs and these fungal pathogens, the receptors expressed on DCs that mediate these responses and the signaling mechanisms that shape the adaptive host response.

Mechanisms of dendritic cell lysosomal killing of Cryptococcus

Cryptococcus neoformans is an opportunistic pulmonary fungal pathogen that disseminates to the CNS causing fatal meningitis in immunocompromised patients. Dendritic cells (DCs) phagocytose C. neoformans following inhalation. Following uptake, cryptococci translocate to the DC lysosomal compartment and are killed by oxidative and non-oxidative mechanisms. DC lysosomal extracts kill cryptococci in vitro; however, the means of antifungal activity remain unknown. Our studies determined non-oxidative antifungal activity by DC lysosomal extract. We examined DC lysosomal killing of cryptococcal strains, anti-fungal activity of purified lysosomal enzymes, and mechanisms of killing against C. neoformans. Results confirmed DC lysosome fungicidal activity against all cryptococcal serotypes. Purified lysosomal enzymes, specifically cathepsin B, inhibited cryptococcal growth. Interestingly, cathepsin B combined with its enzymatic inhibitors led to enhanced cryptococcal killing. Electron microscopy revealed structural changes and ruptured cryptococcal cell walls following treatment. Finally, additional studies demonstrated that osmotic lysis was responsible for cryptococcal death.

The acute neutrophil response mediated by S100 alarmins during vaginal Candida infections is independent of the Th17-pathway

Vulvovaginal candidiasis (VVC) caused by Candida albicans affects a significant number of women during their reproductive ages. Clinical observations revealed that a robust vaginal polymorphonuclear neutrophil (PMN) migration occurs in susceptible women, promoting pathological inflammation without affecting fungal burden. Evidence to date in the mouse model suggests that a similar acute PMN migration into the vagina is mediated by chemotactic S100A8 and S100A9 alarmins produced by vaginal epithelial cells in response to Candida. Based on the putative role for the Th17 response in mucosal candidiasis as well as S100 alarmin induction, this study aimed to determine whether the Th17 pathway plays a role in the S100 alarmin-mediated acute inflammation during VVC using the experimental mouse model. For this, IL-23p19(-/-), IL-17RA(-/-) and IL-22(-/-) mice were intravaginally inoculated with Candida, and vaginal lavage fluids were evaluated for fungal burden, PMN infiltration, the presence of S100 alarmins and inflammatory cytokines and chemokines. Compared to wild-type mice, the cytokine-deficient mice showed comparative levels of vaginal fungal burden and PMN infiltration following inoculation. Likewise, inoculated mice of all strains with substantial PMN infiltration exhibited elevated levels of vaginal S100 alarmins in both vaginal epithelia and secretions in the vaginal lumen. Finally, cytokine analyses of vaginal lavage fluid from inoculated mice revealed equivalent expression profiles irrespective of the Th17 cytokine status or PMN response. These data suggest that the vaginal S100 alarmin response to Candida does not require the cells or cytokines of the Th17 lineage, and therefore, the immunopathogenic inflammatory response during VVC occurs independently of the Th17-pathway.

Cytokines in the host response to Candida vaginitis: Identifying a role for non-classical immune mediators, S100 alarmins

Vulvovaginal candidiasis (VVC), caused by Candida albicans, affects a significant number of women during their reproductive years. More than two decades of research have been focused on the mechanisms associated with susceptibility or resistance to symptomatic infection. Adaptive immunity by Th1-type CD4(+) T cells and downstream cytokine responses are considered the predominant host defense mechanisms against mucosal Candida infections. However, numerous clinical and animal studies have indicated no or limited protective role of cells and cytokines of the Th1 or Th2 lineage against vaginal infection. The role for Th17 is only now begun to be investigated in-depth for VVC with results already showing significant controversy. On the other hand, a clinical live-challenge study and an established animal model have shown that a symptomatic condition is intimately associated with the vaginal infiltration of polymorphonuclear leukocytes (PMNs) but with no effect on vaginal fungal burden. Subsequent studies identified S100A8 and S100A9 alarmins as key chemotactic mediators of the acute PMN response. These chemotactic danger signals appear to be secreted by vaginal epithelial cells upon interaction and early adherence of Candida. Thus, instead of a putative immunodeficiency against Candida involving classical immune cells and cytokines of the adaptive response, the pathological inflammation in VVC is now considered a consequence of a non-productive innate response initiated by non-classical immune mediators.

Protocols for vaginal inoculation and sample collection in the experimental mouse model of Candida vaginitis

Vulvovaginal candidiasis (VVC), caused by Candida species, is a fungal infection of the lower female genital tract that affects approximately 75% of otherwise healthy women during their reproductive years. Predisposing factors include antibiotic usage, uncontrolled diabetes and disturbance in reproductive hormone levels due to pregnancy, oral contraceptives or hormone replacement therapies. Recurrent VVC (RVVC), defined as three or more episodes per year, affects a separate 5 to 8% of women with no predisposing factors. An experimental mouse model of VVC has been established and used to study the pathogenesis and mucosal host response to Candida. This model has also been employed to test potential antifungal therapies in vivo. The model requires that the animals be maintained in a state of pseudoestrus for optimal Candida colonization/infection. Under such conditions, inoculated animals will have detectable vaginal fungal burden for weeks to months. Past studies show an extremely high parallel between the animal model and human infection relative to immunological and physiological properties. Differences, however, include a lack of Candida as normal vaginal flora and a neutral vaginal pH in the mice. Here, we demonstrate a series of key methods in the mouse vaginitis model that include vaginal inoculation, rapid collection of vaginal specimens, assessment of vaginal fungal burden, and tissue preparations for cellular extraction/isolation. This is followed by representative results for constituents of vaginal lavage fluid, fungal burden, and draining lymph node leukocyte yields. With the use of anesthetics, lavage samples can be collected at multiple time points on the same mice for longitudinal evaluation of infection/colonization. Furthermore, this model requires no immunosuppressive agents to initiate infection, allowing immunological studies under defined host conditions. Finally, the model and each technique introduced here could potentially give rise to use of the methodologies to examine other infectious diseases of the lower female genital tract (bacterial, parasitic, viral) and respective local or systemic host defenses.

CD4⁺ T-cell immunity in the female genital tract is critically dependent on local mucosal immunization

Immunizations via the i.n. and intravaginal (ivag) routes effectively generate strong genital tract antibody-mediated immunity. To what extent the same is true for T-cell responses is incompletely known. Therefore, we set out to investigate optimal conditions for stimulation of genital tract CD4(+) T-cell responses, using adoptive transfer of mouse DO11.10 TCR transgenic T cells specific for OVA and OVA conjugated to cholera toxin (CT) as an immunogen. We observed that progesterone was required for a T-cell response following ivag immunization, whereas estradiol prevented a response. Although i.n. immunization stimulated OVA-specific CD4(+) T-cell responses in the draining LNs, it was substantially less effective compared to ivag. More importantly, an ivag booster immunization was absolutely required to attract T cells to the genital tract mucosa itself. While clinical use of CT is precluded because of its toxicity, we developed a combined adjuvant vector based on a non-toxic derivative of CT and immune-stimulating complexes. The CTA1-DD/immune-stimulating complexes (ISCOMs) adjuvant together with major outer membrane protein was effective at stimulating genital tract CD4(+) T-cell immunity and protection against a live chlamydial infection, which holds promise for the development of mucosal vaccines against sexually transmitted infections.

Candida albicans yeast and hyphae are discriminated by MAPK signaling in vaginal epithelial cells

We previously reported that a bi-phasic innate immune MAPK response, constituting activation of the mitogen-activated protein kinase (MAPK) phosphatase MKP1 and c-Fos transcription factor, discriminates between the yeast and hyphal forms of Candida albicans in oral epithelial cells (ECs). Since the vast majority of mucosal Candida infections are vaginal, we sought to determine whether a similar bi-phasic MAPK-based immune response was activated by C. albicans in vaginal ECs. Here, we demonstrate that vaginal ECs orchestrate an innate response to C. albicans via NF-κB and MAPK signaling pathways. However, unlike in oral ECs, the first MAPK response, defined by c-Jun transcription factor activation, is delayed until 2 h in vaginal ECs but is still independent of hypha formation. The 'second' or 'late' MAPK response, constituting MKP1 and c-Fos transcription factor activation, is identical to oral ECs and is dependent upon both hypha formation and fungal burdens. NF-κB activation is immediate but independent of morphology. Furthermore, the proinflammatory response in vaginal ECs is different to oral ECs, with an absence of G-CSF and CCL20 and low level IL-6 production. Therefore, differences exist in how C. albicans activates signaling mechanisms in oral and vaginal ECs; however, the activation of MAPK-based pathways that discriminate between yeast and hyphal forms is retained between these mucosal sites. We conclude that this MAPK-based signaling pathway is a common mechanism enabling different human epithelial tissues to orchestrate innate immune responses specifically against C. albicans hyphae.

Prospects for development of a vaccine to prevent and control vaginal candidiasis

A vaccine against recurrent vulvovaginal candidiasis (RVVC) would benefit a large number of women who suffer from this debilitating syndrome. To date, several antigen formulations have been tested with modest results. In this article, we review the latest vaccine study reported in the literature. The candidate is a β-glucan conjugate administered with a human compatible adjuvant. Results in a mouse model of vaginitis were again modest for protection. However, the study included live animal imaging to quantify fungal burden; animals were challenged with a Candida strain carrying a gene encoding a glycophosphatidylinositol (GPI)-linked cell wall protein and luciferase. Fungal burden was expressed as photons following substrate administration. Protection appeared to be mediated by β-glucan antibodies. Although modest protection was observed, the imaging system was less variable than semi-quantitative plate counts of vaginal lavage fluid. Despite these advances in evaluating protection, a vaccine candidate against RVVC worthy of clinical testing remains elusive.

Epithelial cell-derived S100 calcium-binding proteins as key mediators in the hallmark acute neutrophil response during Candida vaginitis

Vulvovaginal candidiasis (VVC), caused by Candida species, is a significant problem in women of childbearing age. Similar to clinical observations, a robust vaginal polymorphonuclear neutrophil (PMN) migration occurs in a subset of mice without affecting vaginal fungal burden. We hypothesize that the vaginal PMN infiltrate and accompanying inflammation are not protective but instead are responsible for the symptoms of infection. The purpose of this study was to identify the signal(s) associated with the PMN response in the established mouse model. Vaginal lavage fluid from inoculated mice were categorized base on PMN counts, evaluated for PMN chemotactic activity and analyzed by SDS-PAGE and mass spectrometry (MS) for unique protein identification. The lavage fluid from inoculated mice with high, but not low, PMN levels showed increased chemotactic activity. Likewise, SDS-PAGE of lavage fluid with high PMN levels showed distinct protein patterns. MS revealed that bands at 6 and 14 kDa matched the PMN chemotactic calcium-binding proteins (CBPs), S100A8 and S100A9, respectively. The presence of the CBPs in lavage fluid was confirmed by Western blots and enzyme-linked immunosorbent assay. Vaginal tissues and epithelial cells from inoculated mice with high PMN levels stained more intensely and exhibited increased mRNA transcripts for both proteins compared to those in mice with low PMN levels. Subsequent antibody neutralization showed significant abrogation of the chemotactic activity when the lavage fluid was treated with anti-S100A8, but not anti-S100A9, antibodies. These results reveal that the PMN chemotactic CBP S100A8 and S100A9 are produced by vaginal epithelial cells following interaction with Candida and that S100A8 is a strong candidate responsible for the robust PMN migration during experimental VVC.

Patterns of Expression of Vaginal T-Cell Activation Markers during Estrogen-Maintained Vaginal Candidiasis

: The immunosuppressive activity of estrogen was further investigated by assessing the pattern of expression of CD25, CD28, CD69, and CD152 on vaginal T cells during estrogen-maintained vaginal candidiasis. A precipitous and significant decrease in vaginal fungal burden toward the end of week 3 postinfection was concurrent with a significant increase in vaginal lymphocyte numbers. During this period, the percentage of CD3+, CD3+CD4+, CD152+, and CD28+ vaginal T cells gradually and significantly increased. The percentage of CD3+ and CD3+CD4+ cells increased from 43% and 15% at day 0 to 77% and 40% at day 28 postinfection. Compared with 29% CD152+ vaginal T cells in naive mice, > 70% of vaginal T cells were CD152+ at day 28 postinfection. In conclusion, estrogen-maintained vaginal candidiasis results in postinfection time-dependent changes in the pattern of expression of CD152, CD28, and other T-cell markers, suggesting that T cells are subject to mixed suppression and activation signals.

The case for extrathymic development of vaginal T lymphocytes

The vaginal tract mucosa is populated by a small, yet phenotypically diverse and functionally significant, subset of T cells that plays a major role in local cell-mediated immunity. Although phenotypic and functional characteristics of vaginal T cells have received some attention in recent years, little is known about the development of this cell population. In this mini review, the developmental origins of vaginal T cells are traced from published work related to vaginal T cells, the vaginal mucosa environment and vaginal tract infection animal models. A CD3(+)TCR(+)CD2(+)CD5(+)B220(-) (CD3(+)B220(-)) subpopulation, which is mostly CD4(+), makes up 30-40% of vaginal T lymphocytes. This population consists of a TCRalphabeta(+) subset and TCRgammadelta(+) subset. While CD3(+)B220(-)TCRalphabeta(+) vaginal T cells exhibit phenotypic and functional properties consistent with that of peripheral T cells, CD3(+)B220(-)TCRgammadelta(+) vaginal T cells exhibit unique phenotypic and functional features that set them apart from other TCRgammadelta(+) T cell subsets populating the periphery or other mucosal areas. The vaginal mucosa is populated also by CD3(+)TCRalphabeta(+)CD4(-)/8(-)B220(+)CD2(-)CD5(-) T cells (CD3(+)B220(+)) whose relative predominance increases significantly in systemic T cell deficiency. This subset is generally unresponsive to TCR-mediated stimuli and expresses high levels of CD25, perhaps indicative of a regulatory role. Current data suggest that, while CD3(+)B220(-) vaginal T cells are mostly thymic in origin, CD3(+)TCRalphabeta(+)B220(+) cells are exclusively extrathymic.

Systemic and mucosal immunization with Candida albicans hsp90 elicits hsp90-specific humoral response in vaginal mucosa which is further enhanced during experimental vaginal candidiasis

The Candida albicans heat shock protein 90 kDa (hsp90-CA) is an important target for protective antibodies in disseminated candidiasis of experimental mice and humans. Hsp90-CA is present in the cell wall of Candida pseudohyphae or hyphae--typical pathogenic morphotypes in both mucosal and systemic Candida infections. However, the potential protective effects of hsp90-CA-specific antibodies in vaginal candidiasis has not yet been reported. In the present study we used various vaccine formulations (recombinant hsp90-CA protein and hsp90-CA-encoding DNA vaccine) and routes of administration (intradermal, intranasal, and intravenous) to induce both hsp90-CA-specific systemic and vaginal mucosa immune responses in experimental BALB/c mice. The results showed that intradermal recombinant hsp90-CA protein priming, followed by intranasal or intradermal recombinant hsp90-CA protein boosting induced significant increases in both serum and vaginal hsp90-CA-specific IgG and IgA antibodies compared to the control group, as well as enhanced hsp90-CA-specific splenocyte responses in vitro. In the intradermally boosted group, subsequent experimental vaginal Candida infection induced additional increases in the hsp90-CA specific IgG isotype, suggesting that Candida has the ability to induce a local hsp90-specific antibody (IgG) response during vulvovaginal candidiasis. Further work is required to elucidate the importance of immunity to highly conserved antigens during infection of the human female reproductive tract where a balance between immunity to and tolerance for commonly antigens such as hsp90 is necessary for the maintenance of fertility.

Prostaglandin E2 modulates dendritic cell function during chlamydial genital infection

Inflammatory responses mediated by antigen-presenting dendritic cells (DCs), can be modulated by the presence of prostaglandins (PG), including prostaglandin E2 (PGE2). PGE2 modifies the production of an immune response by altering DC function through PGE2 receptors. PGE2 is produced by epithelial cells lining the murine female reproductive tract during Chlamydia muridarum infection and likely manipulates the antichlamydial immune response during antigen uptake in the genital mucosa. Our data demonstrate that the PGE2 present locally in the genital tract upon chlamydial genital infection enhanced the recruitment of CD11b+ conventional DCs, but not CD45R+ plasmacytoid DCs, to infected genital tract tissue and draining lymph nodes in vivo. Furthermore, exposure to PGE2 in vitro during infection of murine bone-marrow-derived conventional DCs (cDCs) boosted interleukin-10 mRNA and protein while not influencing interleukin-12p40 production. Infection of cDCs markedly increased mRNA production of the costimulatory molecules CD86, CD40 and a member of the C-type lectin family, DEC-205, but addition of PGE2 increased other costimulatory molecules and C-type lectins. Also, exposure of PGE2 to infected cDCs increased FcgammaRIII and FcgammaRIIb, suggesting that PGE2 enhances the uptake and presentation of C. muridarum and augments production of the antichlamydial adaptive immune response. Taken together, the data suggest that exposure of infected cDCs to PGE2 drives production of a diverse adaptive immune response with implications for regulating tissue inflammation.

Dendritic cell activation and maturation induced by mucosal fluid from women with bacterial vaginosis

Dendritic cells (DC) at mucosal surfaces mature when exposed to "danger" signals such as LPS. Bacterial vaginosis (BV) is a prevalent alteration of the vaginal bacterial flora associated with preterm childbirth and increased risk for HIV acquisition. We examined the effect of mucosal fluid from women with BV or healthy flora on DC function. IL-12, IL-23 and p40 production by monocyte-derived dendritic cells (MDDC) were all induced by BV samples. Activation/maturation markers HLA-DR, CD40 and CD83 on MDDC incubated with BV CVL were also induced. BV CVL also decreased the endocytic ability of MDDC and increased proliferation of T cells in allogeneic MLR. Plasmacytoid dendritic cell (pDC) CD86 expression was induced by BV CVL. Healthy flora CVL had little effect in any of the tests. This study suggests that BV, but not healthy flora, affects local dendritic cell function in vivo suggesting a mechanism through which BV affects mucosal immunity.

History and update on host defense against vaginal candidiasis

Vulvovaginal candidiasis (VVC), caused by Candida albicans, remains a significant problem in women of childbearing age. While cell-mediated immunity is considered the predominant host defense mechanism against mucosal candidal infections, two decades of research from animal models and clinical studies have revealed a lack of a protective role for adaptive immunity against VVC caused by putative immunoregulatory mechanisms. Moreover, natural protective mechanisms and factors associated with susceptibility to infection have remained elusive. That is until recently, when through a live challenge model in humans, it was revealed that protection against vaginitis coincides with a non-inflammatory innate presence, whereas symptomatic infection correlates with a neutrophil infiltrate in the vaginal lumen and elevated fungal burden. Thus, instead of VVC being caused by a putative deficient adaptive immune response, it is now being considered that symptomatic vaginitis is caused by an aggressive innate response.

Bacterial vaginosis and host immunity

Bacterial vaginosis (BV) has been associated with severe medical consequences including induction of preterm birth and increasing susceptibility to infection by HIV and other genital tract pathogens. Although the mechanism by which BV induces these changes is not yet fully defined, the presence of BV is accompanied by immunologic changes in the lower genital tract environment. The most striking change is the induction of higher levels of proinflammatory cytokines, although this is not accompanied by increased levels of neutrophils. Increased cytokine levels are likely induced by bacterial products present in BV through innate immune recognition pathways such as the toll-like receptors. Recent studies show that changes in HIV susceptibility and HIV detection are associated with changes in bacterial flora. Further research is needed to identify the relative contributions of immune pathways and bacterial flora toward the pathogenic alterations that occur in BV.