Immune Regulation and Its Role in the Pathogenesis of Candida Vaginitis

Novel Mechanism behind the Immunopathogenesis of Vulvovaginal Candidiasis: "Neutrophil Anergy"

For over 3 decades, investigators have studied the pathogenesis of vulvovaginal candidiasis (VVC) and recurrent VVC (RVVC) through clinical studies and animal models. While there was considerable consensus that susceptibility was not associated with any apparent deficiencies in adaptive immunity, protective immune mechanisms and the role of innate immunity remained elusive. It was not until an innovative live-challenge design was conducted in women that a fuller understanding of the natural history of infection/disease was achieved. These studies revealed that symptomatic infection is associated with recruitment of polymorphonuclear neutrophils (PMNs) into the vaginal lumen. Subsequent studies in the established mouse model demonstrated that infiltrating PMNs were incapable of reducing the fungal burden, which supported the hypothesis that VVC/RVVC was an immunopathology, whereby Candida and the host response drive symptomatic disease. Further studies in mice revealed the requirement for C. albicans hyphae and identified pattern recognition receptors (PRRs) and proinflammatory mediators responsible for the PMN response, all of which are critical pieces of the immunopathogenesis. However, a mechanism explaining PMN dysfunction at the vaginal mucosa remained an enigma. Ultimately, by employing mouse strains resistant or susceptible to chronic VVC, it was determined that heparan sulfate (HS) in the vaginal environment of susceptible mice serves as a competitive ligand for Mac-1 on PMNs, which effectively renders the PMNs incapable of binding to Candida to initiate killing. Hence, the outcome of symptomatic VVC/RVVC is postulated to be dependent on a PMN-mediated immunopathogenic response involving HS that effectively places the neutrophils in a state of functional anergy.

Candida albicans Pathogenesis: Fitting within the Host-Microbe Damage Response Framework

Historically, the nature and extent of host damage by a microbe were considered highly dependent on virulence attributes of the microbe. However, it has become clear that disease is a complex outcome which can arise because of pathogen-mediated damage, host-mediated damage, or both, with active participation from the host microbiota. This awareness led to the formulation of the damage response framework (DRF), a revolutionary concept that defined microbial virulence as a function of host immunity. The DRF outlines six classifications of host damage outcomes based on the microbe and the strength of the immune response. In this review, we revisit this concept from the perspective of Candida albicans, a microbial pathogen uniquely adapted to its human host. This fungus commonly colonizes various anatomical sites without causing notable damage. However, depending on environmental conditions, a diverse array of diseases may occur, ranging from mucosal to invasive systemic infections resulting in microbe-mediated and/or host-mediated damage. Remarkably, C. albicans infections can fit into all six DRF classifications, depending on the anatomical site and associated host immune response. Here, we highlight some of these diverse and site-specific diseases and how they fit the DRF classifications, and we describe the animal models available to uncover pathogenic mechanisms and related host immune responses.

Dermatomycoses and inflammation: The adaptive balance between growth, damage, and survival

Dermatomycosis is characterized by both superficial and subcutaneous infections of keratinous tissues and mucous membranes caused by a variety of fungal agents, the two most common classes being dermatophytes and yeasts. Overall, the stepwise process of host infection is similar among the main dermatomycotic species; however, the species-specific ability to elicit a host reaction upon infection is distinct. Yeasts such as Candida albicans elicit a relatively low level of host tissue damage and inflammation during pathogenic infection, while dermatophytes may induce a higher level of tissue damage and inflammatory reaction. Both pathogens can, however, manipulate the host's immune response, ensuring survival and prolonging chronic infection. One common element of most dermatomycotic infections is the disease burden caused by inflammation and associated signs and symptoms, such as erythema, burning and pruritus. There is a strong clinical rationale for the addition of a topical corticosteroid agent to an effective antimycotic therapy, especially in patients who present with inflammatory dermatomycoses (e.g., tinea inguinalis). In this review, we aim to compare the pathogenesis of common dermatomycotic species, including Candida yeasts (Candida albicans), dermatophytes (Trichophyton, Epidermophyton or Microsporum species), and other pathogenic yeasts (Malassezia), with a special focus on unique species-specific aspects of the respective infection processes, the interaction between essential aspects of pathogenic infection, the different roles of the host inflammatory response, and the clinical consequences of the infection-related tissue damage and inflammation. We hope that a broader understanding of the various mechanisms of dermatomycoses may contribute to more effective management of affected patients.

Interaction between interleukin-1 receptor 2 and Toll-like receptor 4, and cervical cytokines

The objective was to assess the impact of genetic variation on cervical cytokine concentrations of interleukin (IL)-1α, IL-1β, IL-6, IL-8 and tumor necrosis factor alpha (TNF-α), and first, to determine if these variants interact with polymorphisms in Toll-like receptor 4 (TLR4) that were previously shown to associate with pro-inflammatory cervical cytokine concentrations, and second, to determine if findings are affected by bacterial vaginosis (BV). We examined 183 single nucleotide polymorphisms (SNPs) in 13 cytokine genes and receptors for associations with cervical cytokine levels in 188 African American and European American women. We tested for associations of gene-gene interactions between SNPs in TLR4 and cytokine gene and receptor polymorphisms with cervical pro-inflammatory cytokines. None of the single locus associations were significant after correction for multiple testing in either European Americans or African Americans. However, there were significant gene-gene interactions between IL-1R2 rs485127 and two SNPs in TLR4 (rs1554973 and rs7856729) with IL-1β after correction for multiple testing. Our study demonstrates that interactions between TLR4 and IL-1R2 are associated with cervical pro-inflammatory cytokine concentrations. These results provide important insights into the possible regulatory mechanisms of the inflammatory response in the presence and absence of microbial disorders such as BV. Additionally, the observed differences in allele frequencies between African Americans and those of European descent may partially explain population disparity in pregnancy-related phenotypes that are cytokine concentration-dependent.

Genetic association of Toll-like receptor 4 with cervical cytokine concentrations during pregnancy

Toll-like receptors (TLRs) are critical components of innate immunity, recognizing bacterial microorganisms and initiating local inflammatory responses. In this study, we assessed the impact of genetic variation in TLR genes on cervical concentrations of pro- and anti-inflammatory cytokines, and determined whether this relationship is influenced by bacterial vaginosis (BV). A total of 4 single nucleotide polymorphisms (SNPs) in TLR2 and 12 in TLR4 were examined for associations with 10 cervical pro- and anti-inflammatory cytokine concentrations in 91 African-American (AA) and 97 European-American (EA) women in the first trimester of pregnancy. In EAs, individuals with the TT genotype at rs1554973 (TLR4) had higher cervical concentrations of interleukin-1 beta (IL-1b) compared with those with the CT or TT genotypes (P=1.5 x 10(-5)), which remains significant after correction for multiple testing. This association was more significant in women with BV (P=5 x 10(-3)) than those without BV (P=0.02). This SNP was also associated with cervical concentrations of IL-1a, IL-6, IL-8 and IP10 (interferon-gamma-inducible protein 10) (P=6 x 10(-3), 0.03, 0.05, 6 x 10(-3), respectively). Our study demonstrates that TLR4 is an important mediator of pro-inflammatory cervical immune responses, particularly in EA women and especially in those with microbial disorders such as BV.

Cervical cytokine network patterns during pregnancy: the role of bacterial vaginosis and geographic ancestry

Few studies have examined the coordinated regulation of the extensive network of cytokines, chemokines, and growth factors involved in the immune response to bacterial vaginosis (BV) during pregnancy. We compared these patterns between women with (BV(+)) and without (BV(-)) bacterial vaginosis and between women of African and of European ancestry. This cohort included 83 Whites (28 BV(+) and 55 BV(-)) and 80 Blacks (41 BV(+) and 39 BV(-)). Pairwise correlations were determined for 28 factors that included cytokines, chemokines, and growth factors. In Whites, there were significantly more correlations involving immunoregulatory cytokines in BV(-) compared with BV(+) women. In Blacks, there were no significant differences in the correlation patterns between BV(+) and BV(-) women. Overall, in BV(-) women, there were no significant differences in the correlation patterns between Whites and Blacks. Conversely, in BV(+) women, Blacks have a stronger correlated response to infection than Whites. This indicates that Whites and Blacks have different correlated immune responses to BV that may at least partially explain the disparity observed in the prevalence of this disease.

Rethinking T cell immunity in oropharyngeal candidiasis

The disproportionate increase in oropharyngeal candidiasis (OPC) compared with systemic and vaginal candidiasis in female patients with AIDS has been a paradox for almost three decades. New data now show that severe OPC develops in Th17-deficient mice, but not Th1-deficient mice, implicating Th17-induced effector molecules in resistance to oral disease. These findings clarify and extend our current thinking about how CD4 T cell deficiency influences susceptibility to OPC.

Perceived stress in women with recurrent vulvovaginal candidiasis

OBJECTIVE

Recurrent vulvovaginal candidiasis (RVVC) has become very common. The aim of this study was to evaluate if women with RVVC perceive more signs of chronic stress than healthy control subjects.

STUDY DESIGN

Thirty-three women with RVVC and 28 healthy control subjects completed a questionnaire about perceived stress at work and in private life, and a health questionnaire. A comparison of the results was performed with the one-way ANOVA test.

RESULTS

More women with RVVC than control subjects reported signs of burnout (p < 0.001), emotional symptoms of stress (p < 0.005), impaired balance between work and leisure time (p = 0.01), bodily symptoms of stress (p < 0.05), worrying factors at work (p < 0.05), and presented type D-personality (p < 0.05).

CONCLUSIONS

The results of this pilot study showed higher degree of perceived stress in women with RVVC compared with healthy controls. These results are in line with our earlier findings of blunted morning rise cortisol and lower mean levels of cortisol in women with RVVC compared with healthy controls.

Modulation of vaginal immune response among pregnant women with bacterial vaginosis by Trichomonas vaginalis, Chlamydia trachomatis, Neisseria gonorrhoeae, and yeast

OBJECTIVE

This study was undertaken to examine the influence of coinfections on vaginal innate and adaptive immunity, and microbial enzyme activities of pregnant women with bacterial vaginosis (BV).

STUDY DESIGN

The population consisted of 265 singleton pregnant women in early gestation (<20 weeks) with BV (Nugent 7-10) who had vaginal fluid collected for measurement of interleukin-1beta (IL-1beta) and IL-8 concentrations, number of neutrophils, immunoglobulin A against Gardnerella vaginalis (anti-Gvh IgA), and activities of microbial sialidase and prolidase.

RESULTS

Among women with BV, median levels of vaginal IL-1beta (4-fold, P = .005), IL-8 (4-fold, P < .001), and neutrophils (6-fold, P = .013) were greatly increased in women with T vaginalis with respect to women without any coinfection. Yeast increased the level of IL-8 (5-fold, P < .001), but not IL-1beta (P = .239) and neutrophils (P = .060). Chlamydia trachomatis and Neisseria gonorrhoeae had no effect on vaginal cytokines. None of the coinfections influenced vaginal anti-Gvh IgA, sialidase and prolidase activities.

CONCLUSION

The strong proinflammatory cytokine induction by T. vaginalis may contribute to the observed increase in preterm birth among BV positive women coinfected with T. vaginalis treated with metronidazole.

Vaginal Immunity in Bacterial Vaginosis

Vaginal immunity in response to microbial perturbation is still poorly understood and may be crucial for protection from adverse outcomes associated with bacterial vaginosis (BV). BV is the most prevalent vaginal disorder in adult women worldwide. However, its pathogenesis is still elusive. In BV-positive women, inflammatory signs are scant--approximately 50% of women are asymptomatic. The number of vaginal neutrophils in the BV-positive patient is not increased with respect to healthy women. In contrast, vaginal interleukin (IL)-1beta levels are largely increased. Recent findings indicate that microbial hydrolytic enzymes could be responsible for dampening the expected proinflammatory response cascade after IL-1beta increase. In other words, BV causes a large increase of vaginal IL-1beta, which is not paralleled by an increase of IL-8 levels, suggesting that BV-associated factors specifically dampen IL-8. The impairment of IL-8 increase may explain the absence of neutrophil increase in most women exposed to a massive abnormal anaerobic vaginal colonization (BV). Among BV-positive women, vaginal innate immunity is strongly correlated to a specific adaptive immune response: the immunoglobulin A (IgA) against the hemolysin produced by Gardnerella vaginalis (anti-Gvh IgA), which is the main bacterium present in BV. High anti-Gvh IgA levels are protective for adverse pregnancy outcomes. However, an exaggerated inflammatory response, mainly attributed to genetic polymorphisms, is also implicated in BV-associated adverse outcomes.