Defective IL-17- and IL-22-dependent mucosal host response to Candida albicans determines susceptibility to oral candidiasis in mice expressing the HIV-1 transgene

Oral Cavity and Candida albicans: Colonisation to the Development of Infection

Candida colonisation of the oral cavity increases in immunocompromised individuals which leads to the development of oral candidiasis. In addition, host factors such as xerostomia, smoking, oral prostheses, dental caries, diabetes and cancer treatment accelerate the disease process. Candida albicans is the primary causative agent of this infection, owing to its ability to form biofilm and hyphae and to produce hydrolytic enzymes and candialysin. Although mucosal immunity is activated, from the time hyphae-associated toxin is formed by the colonising C. albicans cells, an increased number and virulence of this pathogenic organism collectively leads to infection. Prevention of the development of infection can be achieved by addressing the host physiological factors and habits. For maintenance of oral health, conventional oral hygiene products containing antimicrobial compounds, essential oils and phytochemicals can be considered, these products can maintain the low number of Candida in the oral cavity and reduce their virulence. Vulnerable patients should be educated in order to increase compliance.

The microbial and host factors that govern Candida gastrointestinal colonization and dissemination

Candida species are among the most prevalent and abundant members of the gut mycobiota, with Candida albicans (CA) being the most prominent member. CA colonizes numerous mucosal surfaces, most notably the gastrointestinal (GI) and genitourinary tracts. In a healthy host, CA is a pathobiont that exists as a commensal but can become pathogenic if the host's immune system becomes suppressed. The microbial and/or host factors that dictate CA's ability to colonize mucosal surfaces and its ability to disseminate remain of great interest. Here, we review the recent advances and insights regarding Candida colonization and dissemination of the mammalian GI tract.

An IL-17F.S65L Knock-In Mouse Reveals Similarities and Differences in IL-17F Function in Oral Candidiasis: A New Tool to Understand IL-17F

Oropharyngeal candidiasis (OPC) is an opportunistic infection of the oral mucosa caused by the commensal fungus Candida albicans IL-17R signaling is essential to prevent OPC in mice and humans, but the individual roles of its ligands, IL-17A, IL-17F, and IL-17AF, are less clear. A homozygous IL-17F deficiency in mice does not cause OPC susceptibility, whereas mice lacking IL-17A are moderately susceptible. In humans, a rare heterozygous mutation in IL-17F (IL-17F.S65L) was identified that causes chronic mucocutaneous candidiasis, suggesting the existence of essential antifungal pathways mediated by IL-17F and/or IL-17AF. To investigate the role of IL-17F and IL-17AF in more detail, we exploited this "experiment of nature" by creating a mouse line bearing the homologous mutation in IL-17F (Ser65Leu) by CRISPR/Cas9. Unlike Il17f^-/- mice that are resistant to OPC, Il17f^S65L/S65L mice showed increased oral fungal burdens similar to Il17a ^-/- mice. In contrast to humans, however, disease was only evident in homozygous, not heterozygous, mutant mice. The mutation was linked to modestly impaired CXC chemokine expression and neutrophil recruitment to the infected tongue but not to alterations in oral antimicrobial peptide expression. These findings suggest mechanisms by which the enigmatic cytokine IL-17F contributes to host defense against fungi. Moreover, because these mice do not phenocopy Il17f^-/- mice, they may provide a valuable tool to interrogate IL-17F and IL-17AF function in vivo in other settings.

Oral epithelial IL-22/STAT3 signaling licenses IL-17-mediated immunity to oral mucosal candidiasis

Oropharyngeal candidiasis (OPC; thrush) is an opportunistic infection caused by the commensal fungus Candida albicans Interleukin-17 (IL-17) and IL-22 are cytokines produced by type 17 lymphocytes. Both cytokines mediate antifungal immunity yet activate quite distinct downstream signaling pathways. While much is now understood about how IL-17 promotes immunity in OPC, the activities of IL-22 are far less well delineated. We show that, despite having similar requirements for induction from type 17 cells, IL-22 and IL-17 function nonredundantly during OPC. We find that the IL-22 and IL-17 receptors are required in anatomically distinct locations within the oral mucosa; loss of IL-22RA1 or signal transducer and activator of transcription 3 (STAT3) in the oral basal epithelial layer (BEL) causes susceptibility to OPC, whereas IL-17RA is needed in the suprabasal epithelial layer (SEL). Transcriptional profiling of the tongue linked IL-22/STAT3 not only to oral epithelial cell proliferation and survival but also, unexpectedly, to driving an IL-17-specific gene signature. We show that IL-22 mediates regenerative signals on the BEL that replenish the IL-17RA-expressing SEL, thereby restoring the ability of the oral epithelium to respond to IL-17 and thus to mediate antifungal events. Consequently, IL-22 signaling in BEL "licenses" IL-17 signaling in the oral mucosa, revealing spatially distinct yet cooperative activities of IL-22 and IL-17 in oral candidiasis.

Post-sepsis immunosuppression depends on NKT cell regulation of mTOR/IFN-γ in NK cells

As treatment of the early, inflammatory phase of sepsis improves, post-sepsis immunosuppression and secondary infection have increased in importance. How early inflammation drives immunosuppression remains unclear. Although IFN-γ typically helps microbial clearance, we found that increased plasma IFN-γ in early clinical sepsis was associated with the later development of secondary Candida infection. Consistent with this observation, we found that exogenous IFN-γ suppressed macrophage phagocytosis of zymosan in vivo, and antibody blockade of IFN-γ after endotoxemia improved survival of secondary candidemia. Transcriptomic analysis of innate lymphocytes during endotoxemia suggested that NKT cells drove IFN-γ production by NK cells via mTORC1. Activation of invariant NKT (iNKT) cells with glycolipid antigen drove immunosuppression. Deletion of iNKT cells in Cd1d-/- mice or inhibition of mTOR by rapamycin reduced immunosuppression and susceptibility to secondary Candida infection. Thus, although rapamycin is typically an immunosuppressive medication, in the context of sepsis, rapamycin has the opposite effect. These results implicated an NKT cell/mTOR/IFN-γ axis in immunosuppression following endotoxemia or sepsis. In summary, in vivo iNKT cells activated mTORC1 in NK cells to produce IFN-γ, which worsened macrophage phagocytosis, clearance of secondary Candida infection, and mortality.

Advances in Understanding Human Genetic Variations That Influence Innate Immunity to Fungi

Fungi are ubiquitous. Yet, despite our frequent exposure to commensal fungi of the normal mammalian microbiota and environmental fungi, serious, systemic fungal infections are rare in the general population. Few, if any, fungi are obligate pathogens that rely on infection of mammalian hosts to complete their lifecycle; however, many fungal species are able to cause disease under select conditions. The distinction between fungal saprophyte, commensal, and pathogen is artificial and heavily determined by the ability of an individual host's immune system to limit infection. Dramatic examples of commensal fungi acting as opportunistic pathogens are seen in hosts that are immune compromised due to congenital or acquired immune deficiency. Genetic variants that lead to immunological susceptibility to fungi have long been sought and recognized. Decreased myeloperoxidase activity in neutrophils was first reported as a mechanism for susceptibility to Candida infection in 1969. The ability to detect genetic variants and mutations that lead to rare or subtle susceptibilities has improved with techniques such as single nucleotide polymorphism (SNP) microarrays, whole exome sequencing (WES), and whole genome sequencing (WGS). Still, these approaches have been limited by logistical considerations and cost, and they have been applied primarily to Mendelian impairments in anti-fungal responses. For example, loss-of-function mutations in CARD9 were discovered by studying an extended family with a history of fungal infection. While discovery of such mutations furthers the understanding of human antifungal immunity, major Mendelian susceptibility loci are unlikely to explain genetic disparities in the rate or severity of fungal infection on the population level. Recent work using unbiased techniques has revealed, for example, polygenic mechanisms contributing to candidiasis. Understanding the genetic underpinnings of susceptibility to fungal infections will be a powerful tool in the age of personalized medicine. Future application of this knowledge may enable targeted health interventions for susceptible individuals, and guide clinical decision making based on a patient's individual susceptibility profile.

Regulation of host-microbe interactions at oral mucosal barriers by type 17 immunity

The oral mucosa is a primary barrier site and a portal for entry of microbes, food, and airborne particles into the gastrointestinal tract. Nonetheless, mucosal immunity at this barrier remains understudied compared with other anatomical barrier sites. Here, we review basic aspects of oral mucosal histology, the oral microbiome, and common and clinically significant diseases that present at oral mucosal barriers. We particularly focus on the role of interleukin-17 (IL-17)/T helper 17 (TH17) responses in protective immunity and inflammation in the oral mucosa. IL-17/TH17 responses are highly relevant to maintaining barrier integrity and preventing pathogenic infections by the oral commensal fungus Candida albicans On the other hand, aberrant IL-17/TH17 responses are implicated in driving the pathogenesis of periodontitis and consequent bone and tooth loss. We discuss distinct IL-17-secreting T cell subsets, emphasizing their regulation and function in oropharyngeal candidiasis and periodontitis.

Th17 cells differentiated with mycelial membranes of Candida albicans prevent oral candidiasis

Candida albicans is a human commensal that causes opportunistic infections. Th17 cells provide resistance against mucosal infection with C. albicans; however, the T cell antigens remain little known. Our final goal is to find effective T cell antigens of C. albicans that are responsible for immunotherapy against candidiasis. Here, we prepared fractions including cytosol, membrane and cell wall from yeast and mycelial cells. Proteins derived from a membrane fraction of mycelial cells effectively induced differentiation of CD4⁺ T cells into IL-17A-producing Th17 cells. To confirm the immunological response in vivo of proteins from mycelial membrane, we performed adoptive transfer experiments using ex vivo stimulated CD4⁺ T cells from IL-17A-GFP reporter mice. Mycelial membrane-differentiated CD4⁺ Th17 cells adoptively transferred intravenously prevented oral candidiasis by oral infection of C. albicans, compared with control anti-CD3-stimulated CD4⁺ T cells. This was confirmed by the clinical score and the number of neutrophils on the infected tissues. These data suggest that effective T cell antigens against candidiasis could be present in the membrane protein fraction of mycelial cells. The design of novel vaccination strategies against candidiasis will be our next step.

Nystatin enhances the immune response against Candida albicans and protects the ultrastructure of the vaginal epithelium in a rat model of vulvovaginal candidiasis

Background

Vulvovaginal candidiasis (VVC) is a common infectious disease of the lower genital tract. Nystatin, a polyene fungicidal antibiotic, is used as a topical antifungal agent for VVC treatment. The aim of the current study was to investigate the possible immunomodulatory effects of nystatin on the vaginal mucosal immune response during Candida albicans infection and examine its role in protection of vaginal epithelial cell (VEC) ultrastructure.

Results

Following infection with C. albicans, IFN-γ and IL-17 levels in VECs were significantly elevated, while the presence of IgG was markedly decreased as compared to uninfected controls (P <  0.05). No significant differences in IL4 expression were observed. After treatment with nystatin, the level of IFN-γ, IL-17 and IgG was dramatically increased in comparison to the untreated group (P <  0.05). Transmission electron microscopy revealed that C. albicans invades the vaginal epithelium by both induced endocytosis and active penetration. Nystatin treatment protects the ultrastructure of the vaginal epithelium. Compared with the untreated C. albicans-infected group, Flameng scores which measure mitochondrial damage of VECs were markedly decreased (P <  0.001) and the number of adhesive and invasive C. albicans was significantly reduced (P <  0.01) after treatment with nystatin.

Conclusions

Nystatin plays a protective role in the host defense against C. albicans by up-regulating the IFN-γ-related cellular response, the IL-17 signaling pathway and possibly through enhancing VEC-derived IgG-mediated immunity. Furthermore, nystatin notably improves the ultramorphology of the vaginal mucosa, partially through the protection of mitochondria ultrastructure in VECs and inhibition of adhesion and invasion by C. albicans. Together, these effects enhance the immune response of the vaginal mucosa against C. albicans and protect the ultrastructure of vaginal epithelium in VVC rats.

A Multifaceted Role of Tryptophan Metabolism and Indoleamine 2,3-Dioxygenase Activity in Aspergillus fumigatus-Host Interactions

Aspergillus fumigatus is the most prevalent filamentous fungal pathogen of humans, causing either severe allergic bronchopulmonary aspergillosis or often fatal invasive pulmonary aspergillosis (IPA) in individuals with hyper- or hypo-immune deficiencies, respectively. Disease is primarily initiated upon the inhalation of the ubiquitous airborne conidia—the initial inoculum produced by A. fumigatus—which are complete developmental units with an ability to exploit diverse environments, ranging from agricultural composts to animal lungs. Upon infection, conidia initially rely on their own metabolic processes for survival in the host’s lungs, a nutritionally limiting environment. One such nutritional limitation is the availability of aromatic amino acids (AAAs) as animals lack the enzymes to synthesize tryptophan (Trp) and phenylalanine and only produce tyrosine from dietary phenylalanine. However, A. fumigatus produces all three AAAs through the shikimate–chorismate pathway, where they play a critical role in fungal growth and development and in yielding many downstream metabolites. The downstream metabolites of Trp in A. fumigatus include the immunomodulatory kynurenine derived from indoleamine 2,3-dioxygenase (IDO) and toxins such as fumiquinazolines, gliotoxin, and fumitremorgins. Host IDO activity and/or host/microbe-derived kynurenines are increasingly correlated with many Aspergillus diseases including IPA and infections of chronic granulomatous disease patients. In this review, we will describe the potential metabolic cross talk between the host and the pathogen, specifically focusing on Trp metabolism, the implications for therapeutics, and the recent studies on the coevolution of host and microbe IDO activation in regulating inflammation, while controlling infection.

EphA2 is an epithelial cell pattern recognition receptor for fungal β-glucans

Oral epithelial cells discriminate between pathogenic and non-pathogenic stimuli, and only induce an inflammatory response when they are exposed to high levels of a potentially harmful microorganism. The pattern recognition receptors (PRRs) in epithelial cells that mediate this differential response are poorly understood. Here, we demonstrate that the ephrin type-A receptor 2 (EphA2) is an oral epithelial cell PRR that binds to exposed β-glucans on the surface of the fungal pathogen Candida albicans. Binding of C. albicans to EphA2 on oral epithelial cells activates signal transducer and activator of transcription 3 and mitogen-activated protein kinase signalling in an inoculum-dependent manner, and is required for induction of a proinflammatory and antifungal response. EphA2 -/- mice have impaired inflammatory responses and reduced interleukin-17 signalling during oropharyngeal candidiasis, resulting in more severe disease. Our study reveals that EphA2 functions as a PRR for β-glucans that senses epithelial cell fungal burden and is required for the maximal mucosal inflammatory response to C. albicans.

Host Control of Fungal Infections: Lessons from Basic Studies and Human Cohorts

In the last few decades, the AIDS pandemic and the significant advances in the medical management of individuals with neoplastic and inflammatory conditions have resulted in a dramatic increase in the population of immunosuppressed patients with opportunistic, life-threatening fungal infections. The parallel development of clinically relevant mouse models of fungal disease and the discovery and characterization of several inborn errors of immune-related genes that underlie inherited human susceptibility to opportunistic mycoses have significantly expanded our understanding of the innate and adaptive immune mechanisms that protect against ubiquitous fungal exposures. This review synthesizes immunological knowledge derived from basic mouse studies and from human cohorts and provides an overview of mammalian antifungal host defenses that show promise for informing therapeutic and vaccination strategies for vulnerable patients.

Pathogenesis of infections in HIV-infected individuals: insights from primary immunodeficiencies

Following infection with almost any given microorganism other than an emerging pathogen, only a minority of individuals develop life-threatening clinical disease, implying that these individuals have some form of immunodeficiency. A growing number of inherited and acquired immunodeficiencies have been deciphered over the last 50 years. HIV infection is probably the best-known acquired immunodeficiency. It emerged about 40 years ago and precipitates various severe infections, the occurrence of which is associated with a fall in circulating CD4⁺ T cells. However, despite the strength of this correlation, infection rates differ between patients with similar levels and durations of CD4⁺ T lymphopenia in the presence or absence of antiretroviral treatment. Moreover, a few infections seem to be less dependent on total CD4⁺ T-cell levels. The fine detail of the mechanisms underlying these infections is unknown. We discuss here how studies of the human genetics and immunology of some of these infections in patients with primary immunodeficiencies (PIDs) have provided unique insights into their molecular and cellular basis. Defects of specific CD4⁺ Th-cell subsets account for some of these infections, as best exemplified by Th1* for mycobacteriosis and Th17 for candidiasis. PIDs are individually rare, but collectively much more common than initially thought, with new disorders being discovered at an ever-increasing pace and a global prevalence worldwide approaching that of HIV infection. Studies of known and new PIDs should make it possible to dissect the pathogenesis of most human infections at an unprecedented level of molecular and cellular precision. The predictive, preventive, and therapeutic implications of studies of immunity to infection in PIDs may extend to HIV-infected patients and patients with infectious diseases in other settings.

The IDO-AhR Axis Controls Th17/Treg Immunity in a Pulmonary Model of Fungal Infection

In infectious diseases, the enzyme indoleamine 2,3 dioxygenase-1 (IDO1) that catalyzes the tryptophan (Trp) degradation along the kynurenines (Kyn) pathway has two main functions, the control of pathogen growth by reducing available Trp and immune regulation mediated by the Kyn-mediated expansion of regulatory T (Treg) cells via aryl hydrocarbon receptor (AhR). In pulmonary paracoccidioidomycosis (PCM) caused by the dimorphic fungus Paracoccidioides brasiliensis, IDO1 was shown to control the disease severity of both resistant and susceptible mice to the infection; however, only in resistant mice, IDO1 is induced by TGF-β signaling that confers a stable tolerogenic phenotype to dendritic cells (DCs). In addition, in pulmonary PCM, the tolerogenic function of plasmacytoid dendritic cells was linked to the IDO1 activity. To further evaluate the function of IDO1 in pulmonary PCM, IDO1-deficient (IDO1^-/-) C57BL/6 mice were intratracheally infected with P. brasiliensis yeasts and the infection analyzed at three postinfection periods regarding several parameters of disease severity and immune response. The fungal loads and tissue pathology of IDO1^-/- mice were higher than their wild-type controls resulting in increased mortality rates. The evaluation of innate lymphoid cells showed an upregulated differentiation of the innate lymphoid cell 3 phenotype accompanied by a decreased expansion of ILC1 and NK cells in the lungs of infected IDO1^-/- mice. DCs from these mice expressed elevated levels of costimulatory molecules and cytokine IL-6 associated with reduced production of IL-12, TNF-α, IL-1β, TGF-β, and IL-10. This response was concomitant with a marked reduction in AhR production. The absence of IDO1 expression caused an increased influx of activated Th17 cells to the lungs with a simultaneous reduction in Th1 and Treg cells. Accordingly, the suppressive cytokines IL-10, TGF-β, IL-27, and IL-35 appeared in reduced levels in the lungs of IDO1^-/- mice. In conclusion, the immunological balance mediated by the axis IDO/AhR is fundamental to determine the balance between Th17/Treg cells and control the severity of pulmonary PCM.

Sequential Dysfunction and Progressive Depletion of Candida albicans-Specific CD4 T Cell Response in HIV-1 Infection

Loss of immune control over opportunistic infections can occur at different stages of HIV-1 (HIV) disease, among which mucosal candidiasis caused by the fungal pathogen Candida albicans (C. albicans) is one of the early and common manifestations in HIV-infected human subjects. The underlying immunological basis is not well defined. We have previously shown that compared to cytomegalovirus (CMV)-specific CD4 cells, C. albicans-specific CD4 T cells are highly permissive to HIV in vitro. Here, based on an antiretroviral treatment (ART) naïve HIV infection cohort (RV21), we investigated longitudinally the impact of HIV on C. albicans- and CMV-specific CD4 T-cell immunity in vivo. We found a sequential dysfunction and preferential depletion for C. albicans-specific CD4 T cell response during progressive HIV infection. Compared to Th1 (IFN-γ, MIP-1β) functional subsets, the Th17 functional subsets (IL-17, IL-22) of C. albicans-specific CD4 T cells were more permissive to HIV in vitro and impaired earlier in HIV-infected subjects. Infection history analysis showed that C. albicans-specific CD4 T cells were more susceptible to HIV in vivo, harboring modestly but significantly higher levels of HIV DNA, than CMV-specific CD4 T cells. Longitudinal analysis of HIV-infected individuals with ongoing CD4 depletion demonstrated that C. albicans-specific CD4 T-cell response was preferentially and progressively depleted. Taken together, these data suggest a potential mechanism for earlier loss of immune control over mucosal candidiasis in HIV-infected patients and provide new insights into pathogen-specific immune failure in AIDS pathogenesis.

HIV infection is closely associated with enhanced host susceptibility to various opportunistic infections (OIs), among which mucosal candidiasis caused by the fungal pathogen Candida albicans (C. albicans) is an early and common manifestation. Even in the era of effective ART, mucosal candidiasis is still a clinically relevant presentation in HIV-infected patients. The underlying mechanisms are not well defined. CD4-mediated immunity is the major host defense mechanism against C. albicans. We here investigated a group of ART naïve, HIV-infected human subjects and examined longitudinally the impact of HIV on C. albicans-specific CD4 T-cell immunity as compared to CD4 T-cell immunity specific for CMV, another opportunistic pathogen that usually does not cause active disease in early HIV infection. We found that C. albicans-specific CD4 T cells were more susceptible to HIV in vivo and were preferentially depleted in progressive HIV-infected individuals as compared to CMV-specific CD4 T cells. Of importance, we also found that in these HIV-infected subjects C. albicans-specific CD4 T cell response manifested a sequential dysfunction with earlier impairment of Th17, but not Th1, functions. Our study suggests an immunological basis that helps explain the earlier and more common onsets of mucosal candidiasis in progressive HIV-infected patients.

Petrolatum: Barrier repair and antimicrobial responses underlying this "inert" moisturizer

BACKGROUND

Petrolatum is a common moisturizer often used in the prevention of skin infections after ambulatory surgeries and as a maintenance therapy of atopic dermatitis (AD). However, the molecular responses induced by petrolatum in the skin have never been assessed.

OBJECTIVE

We sought to define the cutaneous molecular and structural effects induced by petrolatum.

METHODS

Thirty-six healthy subjects and 13 patients with moderate AD (mean SCORAD score, 39) were studied by using RT-PCR, gene arrays, immunohistochemistry, and immunofluorescence performed on control skin, petrolatum-occluded skin, and skin occluded with a Finn chamber only.

RESULTS

Significant upregulations of antimicrobial peptides (S100A8/fold change [FCH], 13.04; S100A9/FCH, 11.28; CCL20/FCH, 8.36; PI3 [elafin]/FCH, 15.40; lipocalin 2/FCH, 6.94, human β-defensin 2 [DEFB4A]/FCH, 4.96; P < .001 for all) and innate immune genes (IL6, IL8, and IL1B; P < .01) were observed in petrolatum-occluded skin compared with expression in both control and occluded-only skin. Application of petrolatum also induced expression of key barrier differentiation markers (filaggrin and loricrin), increased stratum corneum thickness, and significantly reduced T-cell infiltrates in the setting of "normal-appearing" or nonlesional AD skin, which is known to harbor barrier and immune defects.

CONCLUSIONS

Petrolatum robustly modulates antimicrobials and epidermal differentiation barrier measures. These data shed light on the beneficial molecular responses of petrolatum in barrier-defective states, such as AD and postoperative wound care.

Neutrophils Do Not Express IL-17A in the Context of Acute Oropharyngeal Candidiasis

IL-17 protects against pathogens by acting on nonhematopoietic cells to induce neutrophil recruitment through upregulation of chemokines and G-CSF. IL-17- and Th17-deficient humans and mice are susceptible to mucosal Candida albicans infections, linked to impaired neutrophil responses. IL-17 production is traditionally associated with CD4⁺ Th17 cells. However, IL-17 is also expressed during innate responses to facilitate rapid pathogen clearance. Innate IL-17-expressing cells include various lymphocyte-type subsets, including ILC3, NKT, γδ-T and “natural” Th17 (nTh17) cells. Some reports suggest that neutrophils can express IL-17 during fungal infections. Here, we asked whether neutrophils serve as a source of IL-17 during acute oropharyngeal candidiasis (OPC) using an IL-17A fate-tracking reporter mouse. Mice were subjected to OPC for two days, and oral tissue was analyzed by flow cytometry. IL-17A was expressed by γδ-T cells and TCRβ⁺ natural Th17 (nTh17) cells, as recently reported. Although infiltrating neutrophils were recruited to the tongue following infection, they did not express the IL-17A reporter. Moreover, neutrophil-depleted mice exhibited normal transcription of both Il17a and downstream IL-17-dependent gene targets after Candida challenge. Thus, in acute OPC, neutrophils are not a measurable source of IL-17 production, nor are they necessary to trigger IL-17-dependent gene expression, although they are essential for ultimate pathogen control.

Oropharyngeal Candidiasis in HIV Infection: Analysis of Impaired Mucosal Immune Response to Candida albicans in Mice Expressing the HIV-1 Transgene

IL-17-producing Th17 cells are of critical importance in host defense against oropharyngeal candidiasis (OPC). Speculation about defective Th17 responses to oral C. albicans infection in the context of HIV infection prompted an investigation of innate and adaptive immune responses to Candida albicans in transgenic mice expressing the genome of HIV-1 in immune cells and displaying an AIDS-like disease. Defective IL-17 and IL-22-dependent mucosal responses to C. albicans were found to determine susceptibility to OPC in these transgenic mice. Innate phagocytes were quantitatively and functionally intact, and individually dispensable for control of OPC and to prevent systemic dissemination of Candida to deep organs. CD8+ T-cells recruited to the oral mucosa of the transgenic mice limited the proliferation of C. albicans in these conditions of CD4+ T-cell deficiency. Therefore, the immunopathogenesis of OPC in the context of HIV infection involves defective T-cell-mediated immunity, failure of crosstalk with innate mucosal immune effector mechanisms, and compensatory cell responses, which limit Candida infection to the oral mucosa and prevent systemic dissemination.