Impaired dendritic cell maturation and cytokine production in patients with chronic mucocutanous candidiasis with or without APECED

Autoimmune regulator (Aire) deficiency results in reduced memory CD8+ T cells after Listeria monocytogenes infection in a murine model

Homozygous mutations in the autoimmune regulator (AIRE) gene that cripple thymic negative selection of autoreactive T cells result in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). However, how AIRE regulates the T-cell response against foreign pathogens is not well understood. Here, we observed comparable primary CD8+ T cells but a markedly reduced memory T-cell population and protective function in Aire-/- mice compared with wild-type after infection with a strain of recombinant Listeria monocytogenes. In adoptive transfer models, exogenous congenic CD8+ T cells transferred into Aire-/- mice also showed a reduction in the memory T-cell population, indicating an important role for extrathymic Aire-expressing cells in shaping or sustaining memory T cells. Moreover, using a bone marrow chimeric model, we found that Aire expressed in radioresistant cells plays an important role in maintaining the memory phenotype. These results provide important insights into the role of extrathymic Aire in the T-cell response to infection.

Extrathymic AIRE-expressing cells: Friends or foes in autoimmunity and cancer?

Auto-immune regulator (AIRE) is a transcription factor that is mainly known for its crucial role in the thymus. Here, AIRE ensures central tolerance by promoting the expression of peripheral tissue antigens in thymic epithelial cells, which is essential for the negative selection of autoreactive T cells. Intriguingly, AIRE expressing cells have recently been identified in other tissues outside the thymus as well. However, the exact function of these extrathymic AIRE expressing cells (eTACs) remains largely enigmatic. Human eTACs are mainly found in secondary lymphoid tissues under homeostatic conditions, but are also found in pathologies such as the inflamed tissues of patients with autoimmune diseases and in various cancer tissues. eTACs have been demonstrated to express dendritic cell (DC)-like markers, such as MHCII, CD40 and CD127, but also CCR7, IDO and PD-L1. Interestingly, eTACs lack high expression of co-stimulatory molecules, such as CD80 or CD86. In mice, different types of peripheral AIRE expressing cells have been described, including cells with an innate lymphoid cell-like phenotype and antigen presenting cell (APC) function. These findings suggest that eTACs are APCs with the possibility to modulate or inhibit immune responses, which is confirmed by functional murine studies demonstrating the ability of eTACs to induce tolerance in autoreactive T cells. The potential immunomodulatory function of eTACs makes them promising targets to restore tolerance in autoimmunity or improve immunotherapy in cancer settings. Yet, this requires a better understanding of these cells and the molecular mechanisms involved. In this review we aim to summarize the current knowledge and understanding of eTACs, including their putative roles in health and disease.

Candida albicans Modulates Murine and Human Beta Defensin-1 during Vaginitis

Vulvovaginal candidiasis (VVC) and recurrent vulvovaginal candidiasis (RVVC) are two forms of a disease caused by Candida spp. β-defensin (BD) is one of the most important families of antimicrobial peptides in the female genital tract and includes molecules that exert essential local functions as antimicrobial and PMN chemoattractant peptides. However, the information on their role during murine and human VVC and RVVC is limited. Thus, we analyzed the behavior and contribution of BD1 to the local response in a VVC mice model and the local cytokine profile and human BD1 and BD3 expression in cervicovaginal lavage from patients with VVC and RVVC. We demonstrated that, in patients with RVVC BD1, mRNA and protein expression were severely diminished and that the aspartate proteinase and lipase secreted by C. albicans are involved in that decrease. This study provides novel information about the pathogenesis of VVC and describes a highly efficient C. albicans escape strategy for perpetuating the infection; these results may contribute to the development of new or combined treatment approaches.

Tissue-specific autoimmunity controlled by Aire in thymic and peripheral tolerance mechanisms

Tissue-specific autoimmune diseases are assumed to arise through malfunction of two checkpoints for immune tolerance: defective elimination of autoreactive T cells in the thymus and activation of these T cells by corresponding autoantigens in the periphery. However, evidence for this model and the outcome of such alterations in each or both of the tolerance mechanisms have not been sufficiently investigated. We studied these issues by expressing human AIRE (huAIRE) as a modifier of tolerance function in NOD mice wherein the defects of thymic and peripheral tolerance together cause type I diabetes (T1D). Additive huAIRE expression in the thymic stroma had no major impact on the production of diabetogenic T cells in the thymus. In contrast, huAIRE expression in peripheral antigen-presenting cells (APCs) rendered the mice resistant to T1D, while maintaining other tissue-specific autoimmune responses and antibody production against an exogenous protein antigen, because of the loss of Xcr1+ dendritic cells, an essential component for activating diabetogenic T cells in the periphery. These results contrast with our recent demonstration that huAIRE expression in both the thymic stroma and peripheral APCs resulted in the paradoxical development of muscle-specific autoimmunity. Our results reveal that tissue-specific autoimmunity is differentially controlled by a combination of thymic function and peripheral tolerance, which can be manipulated by expression of huAIRE/Aire in each or both of the tolerance mechanisms.

IL-22 neutralizing autoantibodies impair fungal clearance in murine oropharyngeal candidiasis model

Protection against mucocutaneous candidiasis depends on the T helper (Th)17 pathway, as gene defects affecting its integrity result in inability to clear Candida albicans infection on body surfaces. Moreover, autoantibodies neutralizing Th17 cytokines have been related to chronic candidiasis in a rare inherited disorder called autoimmune polyendocriopathy candidiasis ectodermal dystrophy (APECED) caused by mutations in autoimmune regulator (AIRE) gene. However, the direct pathogenicity of these autoantibodies has not yet been addressed. Here we show that the level of anti-IL17A autoantibodies that develop in aged Aire-deficient mice is not sufficient for conferring susceptibility to oropharyngeal candidiasis. However, patient-derived monoclonal antibodies that cross-react with murine IL-22 increase the fungal burden on C. albicans infected mucosa. Nevertheless, the lack of macroscopically evident infectious pathology on the oral mucosa of infected mice suggests that additional susceptibility factors are needed to precipitate a clinical disease.

Chronic immunosuppression in the mature patient

In the ever-aging population of the world, the field of geriatrics continues to grow in importance. As human beings age, the skin undergoes a unique array of changes that predispose it to a specific set of dermatoses, infections, and neoplasms. Some of these physiologic alterations are comparable to the changes that happen in immunosuppressed individuals. Given the importance of immunosuppressive medications in treatment of many common skin conditions, we have reviewed the current literature to assist the practicing clinician in using immunosuppressive medications in the geriatric population.

Altered Immune Activation and IL-23 Signaling in Response to Candida albicans in Autoimmune Polyendocrine Syndrome Type 1

OBJECTIVE

Autoimmune polyendocrine syndrome type 1 (APS-1) is a rare, childhood onset disease caused by mutations in the autoimmune regulator (AIRE) gene. Chronic mucocutaneous candidiasis (CMC) is one of the three major disease components and is, to date, mainly explained by the presence of neutralizing auto-antibodies against cytokines [interleukin (IL)-17A, IL-17F, and IL-22] from T helper 17 cells, which are critical for the protection against fungal infections. However, patients without current auto-antibodies also present CMC and we, therefore, hypothesized that other immune mechanisms contribute to CMC in APS-1.

METHODS

Whole blood was stimulated with Candida albicans (C. albicans) in a standardized assay, and immune activation was investigated by analyzing 46 secreted immune mediators. Then, peripheral blood mononuclear cells were stimulated with curdlan, a Dectin-1 agonist and IL-23 inducer, and the IL-23p19 response in monocytes was analyzed by flow cytometry.

RESULTS

We found an altered immune response in APS-1 patients compared with healthy controls. Patients fail to increase the essential ILs, such as IL-2, IL-17A, IL-22, and IL-23, when stimulating whole blood with C. albicans. A significantly altered IL-23p19 response was detected in patients' monocytes upon stimulation with curdlan.

CONCLUSION

APS-1 patients have an altered immune response to C. albicans including a dysregulation of IL-23p19 production in monocytes. This probably contributes to the selective susceptibility to CMC found in the majority of patients.

Autoreactive T Cells and Chronic Fungal Infection Drive Esophageal Carcinogenesis

Humans with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), a T cell-driven autoimmune disease caused by impaired central tolerance, are susceptible to chronic fungal infection and esophageal squamous cell carcinoma (ESCC). However, the relationship between autoreactive T cells and chronic fungal infection in ESCC development remains unclear. We find that kinase-dead Ikkα knockin mice develop APECED-like phenotypes, including impaired central tolerance, autoreactive T cells, chronic fungal infection, and ESCCs expressing specific human ESCC markers. Using this model, we investigated the link between ESCC and fungal infection. Autoreactive CD4 T cells permit fungal infection and incite tissue injury and inflammation. Antifungal treatment or autoreactive CD4 T cell depletion rescues, whereas oral fungal administration promotes, ESCC development. Inhibition of inflammation or epidermal growth factor receptor (EGFR) activity decreases fungal burden. Fungal infection is highly associated with ESCCs in non-autoimmune human patients. Therefore, autoreactive T cells and chronic fungal infection, fostered by inflammation and epithelial injury, promote ESCC development.

AIRE is not essential for the induction of human tolerogenic dendritic cells

Loss-of-function mutations of the Autoimmune Regulator (AIRE) gene results in organ-specific autoimmunity and disease Autoimmune Polyendocrinopathy type 1 (APS1)/Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED). The AIRE protein is crucial in the induction of central tolerance, promoting ectopic expression of tissue-specific antigens in medullary thymic epithelial cells and enabling removal of self-reactive T-cells. AIRE expression has recently been detected in myeloid dendritic cells (DC), suggesting AIRE may have a significant role in peripheral tolerance. DC stimulation of T-cells is critical in determining the initiation or lack of an immune response, depending on the pattern of costimulation and cytokine production by DCs, defining immunogenic/inflammatory (inflDC) and tolerogenic (tolDC) DC. In AIRE-deficient patients and healthy controls, we validated the role of AIRE in the generation and function of monocyte-derived inflDC and tolDCs by determining mRNA and protein expression of AIRE and comparing activation markers (HLA-DR/DP/DQ,CD83,CD86,CD274(PDL-1),TLR-2), cytokine production (IL-12p70,IL-10,IL-6,TNF-α,IFN-γ) and T-cell stimulatory capacity (mixed lymphocyte reaction) of AIRE+ and AIRE- DCs. We show for the first time that: (1) tolDCs from healthy individuals express AIRE; (2) AIRE expression is not significantly higher in tolDC compared to inflDC; (3) tolDC can be generated from APECED patient monocytes and (4) tolDCs lacking AIRE retain the same phenotype and reduced T-cell stimulatory function. Our findings suggest that AIRE does not have a role in the induction and function of monocyte-derived tolerogenic DC in humans, but these findings do not exclude a role for AIRE in peripheral tolerance mediated by other cell types.

Anticommensal Responses Are Associated with Regulatory T Cell Defect in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy Patients

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autoimmune disease caused by mutations in the AIRE gene. Although mainly an endocrine disease, a substantial fraction of patients have gastrointestinal manifestations. In this study, we have examined the role of anticommensal responses and their regulation. APECED patients had increased levels of Abs against Saccharomyces cerevisiae (p < 0.0001) and against several species of commensal gut bacteria, but not against species predominantly associated with other locations. The anticommensal Ab levels did not correlate with gastrointestinal autoantibodies, neutralizing anti-IL-17 or -IL-22 Abs, or gastrointestinal symptoms, although scarcity of the available clinical data suggests that further study is required. However, the anti-S. cerevisiae Ab levels showed a significant inverse correlation with FOXP3 expression levels in regulatory T cells (Treg), previously shown to be dysfunctional in APECED. The correlation was strongest in the activated CD45RO(+) population (ρ = -0.706; p < 0.01). APECED patients also had decreased numbers of FOXP3(+) cells in gut biopsies. These results show that APECED patients develop early and sustained responses to gut microbial Ags in a pattern reminiscent of Crohn's disease. This abnormal immune recognition of gut commensals is linked to a systemic Treg defect, which is also reflected as a local decrease of gut-associated Treg. To our knowledge, these data are the first to show dysregulated responses to non-self commensal Ags in APECED and indicate that AIRE contributes to the regulation of gut homeostasis, at least indirectly. The data also raise the possibility of persistent microbial stimulation as a contributing factor in the pathogenesis of APECED.

The fungal quorum-sensing molecule farnesol activates innate immune cells but suppresses cellular adaptive immunity

Farnesol, produced by the polymorphic fungus Candida albicans, is the first quorum-sensing molecule discovered in eukaryotes. Its main function is control of C. albicans filamentation, a process closely linked to pathogenesis. In this study, we analyzed the effects of farnesol on innate immune cells known to be important for fungal clearance and protective immunity. Farnesol enhanced the expression of activation markers on monocytes (CD86 and HLA-DR) and neutrophils (CD66b and CD11b) and promoted oxidative burst and the release of proinflammatory cytokines (tumor necrosis factor alpha [TNF-α] and macrophage inflammatory protein 1 alpha [MIP-1α]). However, this activation did not result in enhanced fungal uptake or killing. Furthermore, the differentiation of monocytes to immature dendritic cells (iDC) was significantly affected by farnesol. Several markers important for maturation and antigen presentation like CD1a, CD83, CD86, and CD80 were significantly reduced in the presence of farnesol. Furthermore, farnesol modulated migrational behavior and cytokine release and impaired the ability of DC to induce T cell proliferation. Of major importance was the absence of interleukin 12 (IL-12) induction in iDC generated in the presence of farnesol. Transcriptome analyses revealed a farnesol-induced shift in effector molecule expression and a down-regulation of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor during monocytes to iDC differentiation. Taken together, our data unveil the ability of farnesol to act as a virulence factor of C. albicans by influencing innate immune cells to promote inflammation and mitigating the Th1 response, which is essential for fungal clearance.

Farnesol is a quorum-sensing molecule which controls morphological plasticity of the pathogenic yeast Candida albicans. As such, it is a major mediator of intraspecies communication. Here, we investigated the impact of farnesol on human innate immune cells known to be important for fungal clearance and protective immunity. We show that farnesol is able to enhance inflammation by inducing activation of neutrophils and monocytes. At the same time, farnesol impairs differentiation of monocytes into immature dendritic cells (iDC) by modulating surface phenotype, cytokine release and migrational behavior. Consequently, iDC generated in the presence of farnesol are unable to induce proper T cell responses and fail to secrete Th1 promoting interleukin 12 (IL-12). As farnesol induced down-regulation of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor, desensitization to GM-CSF could potentially explain transcriptional reprofiling of iDC effector molecules. Taken together, our data show that farnesol can also mediate Candida-host communication and is able to act as a virulence factor.

Antifungal Th Immunity: Growing up in Family

Fungal diseases represent an important paradigm in immunology since they can result from either the lack of recognition or over-activation of the inflammatory response. Current understanding of the pathophysiology underlying fungal infections and diseases highlights the multiple cell populations and cell-signaling pathways involved in these conditions. A systems biology approach that integrates investigations of immunity at the systems-level is required to generate novel insights into this complexity and to decipher the dynamics of the host–fungus interaction. It is becoming clear that a three-way interaction between the host, microbiota, and fungi dictates the types of host–fungus relationship. Tryptophan metabolism helps support this interaction, being exploited by the mammalian host and commensals to increase fitness in response to fungi via resistance and tolerance mechanisms of antifungal immunity. The cellular and molecular mechanisms that provide immune homeostasis with the fungal biota and its possible rupture in fungal infections and diseases will be discussed within the expanding role of antifungal Th cell responses.

Human APECED; a Sick Thymus Syndrome?

Loss-of-function mutations in the Autoimmune Regulator (AIRE) gene cause a rare inherited form of autoimmune disease, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, also known as autoimmune polyglandular syndrome type 1. The patients suffer from multiple endocrine deficiencies, the most common manifestations being hypoparathyroidism, Addison’s disease, hypogonadism, and secondary amenorrhea, usually accompanied by typical autoantibodies against the target tissues. Chronic mucocutaneous candidiasis is also a prominent part of the disease. The highest expression of AIRE is found in medullary thymic epithelial cells (mTECs). Murine studies suggest that it promotes ectopic transcription of self antigens in mTECs and is thus important for negative selection. However, failed negative selection alone is not enough to explain key findings in human patients, necessitating the search for alternative or additional pathogenetic mechanisms. A striking feature of the human AIRE-deficient phenotype is that all patients develop high titers of neutralizing autoantibodies against type I interferons, which have been shown to downregulate the expression of interferon-controlled genes. These autoantibodies often precede clinical symptoms and other autoantibodies, suggesting that they are a reflection of the pathogenetic process. Other cytokines are targeted as well, notably those produced by Th17 cells; these autoantibodies have been linked to the defect in anti-candida defenses. A defect in regulatory T cells has also been reported in several studies and seems to affect already the recent thymic emigrant population. Taken together, these findings in human patients point to a widespread disruption of T cell development and regulation, which is likely to have its origins in an abnormal thymic milieu. The absence of functional AIRE in peripheral lymphoid tissues may also contribute to the pathogenesis of the disease.

Inborn errors of human IL-17 immunity underlie chronic mucocutaneous candidiasis

PURPOSE OF REVIEW

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent symptomatic infection of the nails, skin and mucosae mostly by Candida albicans. CMC is common in patients with profound primary T-cell immunodeficiency, who often display multiple infectious and autoimmune diseases. Patients with syndromic CMC, including autosomal dominant hyper IgE syndrome (AD-HIES) and autosomal recessive autoimmune polyendocrinopathy syndrome type I (APS-I), display fewer other infections. Patients with isolated CMC (CMCD) rarely display any other severe disease. We review here recent progress in the genetic dissection of these three types of inherited CMC.

RECENT FINDINGS

Low IL-17 T-cell proportions were reported in patients with AD-HIES bearing heterozygous STAT3 mutations, prone to CMC and staphylococcal diseases, and in a kindred with autosomal recessive CARD9 deficiency, prone to CMC and other fungal infections. High levels of neutralizing autoantibodies against IL-17 cytokines were documented in patients with APS-I presenting with CMC as their only infectious disease. The first three genetic causes of CMCD were then reported: autosomal recessive IL-17RA and autosomal dominant IL-17F deficiencies and autosomal dominant STAT1 gain-of-function, impairing IL-17-producing T-cell development.

SUMMARY

Inborn errors of human IL-17 immunity underlie CMC. Impaired IL-17 immunity may therefore account for CMC in other settings, including patients with acquired immunodeficiency.

Challenges for a universal Staphylococcus aureus vaccine

This review considers the reasons why the staphylococcal vaccine trials may have failed, based on new information about protective immunity against Staphylococcus aureus. The clinical trials and future vaccine candidate antigens are reviewed. Challenges facing the development of a universal S. aureus vaccine are also considered. The lack of a biomarker that is able to predict protection is a major stumbling block in the development of a staphylococcal vaccine. The major new information involves the role of cell-mediated immunity, specifically T-helper 17 cells and interleukin 17, as well as the lack of protection afforded by specific antibodies. This has major implications for future vaccine development and planning of clinical trials.

Expanding the clinical and genetic spectrum of human CD40L deficiency: the occurrence of paracoccidioidomycosis and other unusual infections in Brazilian patients

CD40 ligand (CD40L) deficiency or X-linked hyper-IgM syndrome (X-HIGM) is a well-described primary immunodeficiency in which Pneumocystis jiroveci pneumonia is a common clinical feature. We have identified an unusual high incidence of fungal infections and other not yet described infections in a cohort of 11 X-HIGM patients from nine unrelated Brazilian families. Among these, we describe the first case of paracoccidioidomycosis (PCM) in X-HIGM. The molecular genetic analysis of CD40L was performed by gene sequencing and evaluation of CD40L protein expression. Nine of these 11 patients (82%) had fungal infections. These included fungal species common to CD40L deficiency (P. jiroveci and Candida albicans) as well as Paracoccidioides brasiliensis. One patient presented with PCM at age 11 years and is now doing well at 18 years of age. Additionally, one patient presented with a simultaneous infection with Klebsiella and Acinetobacter, and one with condyloma caused by human papilloma virus. Molecular analysis revealed four previously described CD40L mutations, two novel missense mutations (c.433 T > G and c.476 G > C) resulting in the absence of CD40L protein expression by activated CD4(+) cells and one novel insertion (c.484_485insAA) within the TNFH domain leading to a frame shift and premature stop codon. These observations demonstrated that the susceptibility to fungal infections in X-HIGM extends beyond those typically associated with X-HIGM (P. jiroveci and C. albicans) and that these patients need to be monitored for those pathogens.

Is there a future for a Staphylococcus aureus vaccine?

Multiple attempts to develop a vaccine to prevent Staphylococcus aureus infections have failed. To date, all have been based upon the development of opsonic antibodies. New information suggests that cell mediated immunity may be critical for protection against S. aureus infections. The arm of the immune system that provides the protection contains the Th17/IL-17 axis. Th17 cells release IL-17, which are important for mobilization and activation of neutrophils. Naturally, antibodies aid the neutrophils in the uptake and killing of staphylococci, but immune globulin does not seem to be sufficient to afford protection. New approaches that focus on Th17/IL-17 may allow for the development of a successful S. aureus vaccine.

Defective central tolerance in Aire-deficient mice is not sufficient to induce symptomatic autoimmunity during lymphopenia-induced T cell proliferation

Transcriptional regulator autoimmune regulator (AIRE) controls thymic negative selection but it is also expressed in secondary lymphoid organs. The relative contribution of AIRE's central and peripheral function to the maintenance of tolerance is unclear. We transferred mature lymphocytes from Aire(-/-) or wild-type donors to Aire(+/+) lymphopenic recipients, which allowed us to gauge the autoreactivity inherent in the cells originating in an Aire(-/-) thymus. In the ensuing lymphopenia-induced proliferation (LIP), the recipients of cells from Aire(-/-) showed definite T cell hyperproliferation and developed autoantibodies at a higher frequency than the recipients of wild-type cells. However, neither of the recipient groups developed clinical symptoms, and pathological tissue infiltrates were also absent. The recipients of Aire(-/-) cells showed hyperproliferation and increased accumulation of regulatory T cells (Tregs), especially in tissues susceptible to inflammation triggered by LIP. These data are consistent with the view that T cells developing in the absence of Aire are autoreactive. However, overt autoimmunity was prevented, most likely by the suppressive function of Treg cells in the Aire-sufficient recipients. Our results support the importance of the peripheral AIRE expression in the maintenance of immunological tolerance.

Mucocutaneous candidiasis and autoimmunity against cytokines in APECED and thymoma patients: clinical and pathogenetic implications

Much has been learnt about the mechanisms of thymic self-tolerance induction from work on both the rare autosomal recessive disease autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) and the autoimmune regulator (AIRE) protein mutated in this disease. Normally, AIRE drives low-level expression of huge numbers of peripheral tissue-specific antigens (TSAgs) in medullary thymic epithelial cells (mTECs), leading to the deletion of TSAg-reactive thymocytes maturing nearby. The very recently discovered neutralizing autoantibodies (autoAbs) against Th17-related cells and cytokines in two autoimmunity-related syndromes associated with AIRE-mutant thymi or AIRE-deficient thymomas help to explain the chronic mucocutaneous candidiasis (CMC) seen in both syndromes. The surprising parallels between these syndromes also demand new hypotheses and research into the consequences of AIRE deficiency and the ensuing autoimmunizing pathways, and suggest more appropriate treatment regimens as discussed in this review.

Immunity to fungal infections

Fungal diseases represent an important paradigm in immunology, as they can result from either a lack of recognition by the immune system or overactivation of the inflammatory response. Research in this field is entering an exciting period of transition from studying the molecular and cellular bases of fungal virulence to determining the cellular and molecular mechanisms that maintain immune homeostasis with fungi. The fine line between these two research areas is central to our understanding of tissue homeostasis and its possible breakdown in fungal infections and diseases. Recent insights into immune responses to fungi suggest that functionally distinct mechanisms have evolved to achieve optimal host-fungus interactions in mammals.

Cracking the Toll-like receptor code in fungal infections

Innate control of fungal infection requires the specific recognition of invariant fungal molecular structures by a variety of innate immune receptors, including Toll-like receptors. In addition to the role in inducing protective immune responses, Toll-like receptor engagement may paradoxically favor fungal infections, by inducing inflammatory pathology and impairing antifungal immunity. Although the dissection of complex genetic traits modulating susceptibility to fungal infections is complex, the contribution of host genetics may hold the key to elucidating new risk factors for these severe, often fatal diseases. Understanding host-pathogen interactions at the innate immune interface will eventually lead to the development of new therapeutics and genetic markers in fungal infections.

Pathogenesis and treatment of oral candidosis

Oral infections caused by yeast of the genus Candida and particularly Candida albicans (oral candidoses) have been recognised throughout recorded history. However, since the 1980s a clear surge of interest and associated research into these infections have occurred. This has largely been due to an increased incidence of oral candidosis over this period, primarily because of the escalation in HIV-infection and the AIDS epidemic. In addition, changes in medical practice leading to a greater use of invasive clinical procedures and a more widespread use of immunosuppressive therapies have also contributed to the problem. Whilst oral candidosis has previously been considered to be a disease mainly of the elderly and very young, its occurrence throughout the general population is now recognised. Candida are true ‘opportunistic pathogens’ and only instigate oral infection when there is an underlying predisposing condition in the host. Treatment of these infections has continued (and in some regards continues) to be problematic because of the potential toxicity of traditional antifungal agents against host cells. The problem has been compounded by the emergence of Candida species other than C. albicans that have inherent resistance against traditional antifungals. The aim of this review is to give the reader a contemporary overview of oral candidosis, the organisms involved, and the management strategies that are currently employed or could be utilised in the future.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED) due to AIRET16M mutation in a consanguineous Greek girl

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED) or autoimmune polyendocrine syndrome type 1 (APS-1) is a rare autosomal recessive disease caused by mutations of the AutoImmune REgulator (AIRE) gene, an important mediator of tolerance to self-antigens. It is characterized by two out of three major components: chronic mucocutaneous candidiasis, hypoparathyroidism and Addison's disease. We present an 11-year-old girl suffering from recurrent episodes of mucocutaneous candidiasis and onychomycosis from 1 to 6 years of age, and transient alopecia at the age of 4 years. Hypoparathyroidism and dental enamel hypoplasia were diagnosed at 8 years. Autoantibodies to thyroid and adrenal glands were not detected and all other endocrine functions have remained normal. Genetic analysis revealed that the patient was homozygous for the mutation T16M in exon 1 of the AIRE gene (p.T16M, c.47C>T). This is the first APECED case reported for carrying this mutation in homozygous form. Parents were third cousins and heterozygous carriers of this mutation.

Impaired T(H)17 responses in patients with chronic mucocutaneous candidiasis with and without autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy

BACKGROUND

Accumulating evidence implicates T(H)17 cytokines in protection against Candida species infections, but the clinical relevance is not clear. Chronic mucocutaneous candidiasis (CMC) is a heterogeneous syndrome with the unifying feature of selective susceptibility to chronic candidiasis. Different subgroups with distinct clinical features are recognized, including autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), CMC with hypothyroidism, and isolated CMC. Understanding immune defects in patients with CMC will define cellular and molecular mechanisms crucial for protection against Candida species in human subjects.

OBJECTIVES

We sought to determine whether impaired T(H)17 responses underlie susceptibility to Candida species infections and whether the same defect is present in different CMC subgroups.

METHODS

We assessed T(H)17 responses of PBMCs to Candida and non-Candida species stimuli by measuring IL-17, IL-22, IL-21, IL-6, IL-23, and IFN-γ cytokine production using cytokine arrays and intracellular cytokine-producing cell numbers and proliferation with flow cytometry. PBMCs from healthy subjects and unaffected family members served as controls.

RESULTS

In patients with CMC with hypothyroidism, T(H)17 cells demonstrated decreased proliferation and IL-17 production in response to Candida species. In contrast, in patients with APECED, T(H)17 cell proliferation and IL-17 production were normal unless exposed to APECED plasma, which inhibited both functions in both APECED and normal PBMCs. Candida species-stimulated IL-22 production was impaired in all patients with CMC, whereas IL-6 and IL-23 responses were unaltered.

CONCLUSION

An impaired T(H)17 response to Candida species, although mediated by different mechanisms, was present in all CMC subgroups studied and might be a common factor predisposing to chronic candidiasis.

The role of the IL-12 cytokine family in directing T-cell responses in oral candidosis

Candida albicans is an opportunistic fungal pathogen that normally exists as a harmless commensal in humans. In instances where host debilitation occurs, Candida can cause a range of clinical infections, and whilst these are primarily superficial, effecting mucosal membranes, systemic infections can develop in severely immunocompromised individuals. The mechanism of host immunity during commensal carriage of C. albicans has been intensively studied. In this paper, we present the most recent information concerning host recognition of C. albicans leading to cytokine production and the subsequent T-cell responses generated in response to C. albicans. Particular focus is given to the role of the IL-12 cytokine family including IL-12, IL-23, IL-27, and IL-35, in host immunity to Candida. CD4⁺ T-cells are considered crucial in the regulation of immunity and inflammation. In this regard, the role of Th1/2, helper cells, together with the recently identified Th17 and Treg cells in candidosis will be discussed. Understanding the detailed mechanisms that underlie host immunity to Candida not only will be of benefit in terms of the infections caused by this organism but could also be exploited in the development of therapeutic interventions for other diseases.

Epithelial cells and innate antifungal defense

The human pathogenic fungus Candida albicans is the predominant cause of both superficial and invasive forms of candidiasis. Clinical observations indicate that mucocutaneous Candida infections are commonly associated with defective cell-mediated immune responses. The importance of the innate immune system as a first-line defense against pathogenic challenge has long been recognized. Over the last decade, many key molecules mediating innate host defense have been identified. Central to these developments is the discovery of pattern recognition receptors such as Toll-like receptors and C-type lectin-receptors that induce innate immune responses and also modulate cellular and humoral adaptive immunity during Candida infections. Although a large amount of information is now available in systemic infections, little is known about localized infections. We address the most relevant pattern recognition receptors and their signaling mechanisms in oral epithelial cells, to gain a better understanding of their contributions to antifungal innate immunity.

Chronic mucocutaneous candidiasis in APECED or thymoma patients correlates with autoimmunity to Th17-associated cytokines

Chronic mucocutaneous candidiasis (CMC) is frequently associated with T cell immunodeficiencies. Specifically, the proinflammatory IL-17A-producing Th17 subset is implicated in protection against fungi at epithelial surfaces. In autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED, or autoimmune polyendocrine syndrome 1), CMC is often the first sign, but the underlying immunodeficiency is a long-standing puzzle. In contrast, the subsequent endocrine features are clearly autoimmune, resulting from defects in thymic self-tolerance induction caused by mutations in the autoimmune regulator (AIRE). We report severely reduced IL-17F and IL-22 responses to both Candida albicans antigens and polyclonal stimulation in APECED patients with CMC. Surprisingly, these reductions are strongly associated with neutralizing autoantibodies to IL-17F and IL-22, whereas responses were normal and autoantibodies infrequent in APECED patients without CMC. Our multicenter survey revealed neutralizing autoantibodies against IL-17A (41%), IL-17F (75%), and/ or IL-22 (91%) in >150 APECED patients, especially those with CMC. We independently found autoantibodies against these Th17-produced cytokines in rare thymoma patients with CMC. The autoantibodies preceded the CMC in all informative cases. We conclude that IL-22 and IL-17F are key natural defenders against CMC and that the immunodeficiency underlying CMC in both patient groups has an autoimmune basis.

Autoantibodies against IL-17A, IL-17F, and IL-22 in patients with chronic mucocutaneous candidiasis and autoimmune polyendocrine syndrome type I

Most patients with autoimmune polyendocrine syndrome type I (APS-I) display chronic mucocutaneous candidiasis (CMC). We hypothesized that this CMC might result from autoimmunity to interleukin (IL)-17 cytokines. We found high titers of autoantibodies (auto-Abs) against IL-17A, IL-17F, and/or IL-22 in the sera of all 33 patients tested, as detected by multiplex particle-based flow cytometry. The auto-Abs against IL-17A, IL-17F, and IL-22 were specific in the five patients tested, as shown by Western blotting. The auto-Abs against IL-17A were neutralizing in the only patient tested, as shown by bioassays of IL-17A activity. None of the 37 healthy controls and none of the 103 patients with other autoimmune disorders tested had such auto-Abs. None of the patients with APS-I had auto-Abs against cytokines previously shown to cause other well-defined clinical syndromes in other patients (IL-6, interferon [IFN]-gamma, or granulocyte/macrophage colony-stimulating factor) or against other cytokines (IL-1beta, IL-10, IL-12, IL-18, IL-21, IL-23, IL-26, IFN-beta, tumor necrosis factor [alpha], or transforming growth factor beta). These findings suggest that auto-Abs against IL-17A, IL-17F, and IL-22 may cause CMC in patients with APS-I.

[Dendritic cells in sepsis: an approach to post-infectious immunosuppression]

Dendritic cells (DCs) play a decisive role in the immune system, especially in the initial events that determine coordination between the innate and adaptive response. Moreover, they are antigen-presenting cells which, through contact with T cells, determine the type of immune responses towards inflammatory or anti-inflammatory. Currently, the hypothesis that attributes importance to the development of a post-infectious immunosuppression in the prognosis of the septic patient is growing stronger. It has been possible to verify the role played by these cells in this type of immunosuppression by the significant decrease in the number of DCs and by the dysfunctions in the functional capacity that include, on the one hand, the abnormal cytokine production and, on the other hand, the alterations in communication between the DCs and T cells that constitute an essential immunological fact. Further research into the knowledge regarding the DCs, in the context of severe infection, may help to consolidate some encouraging data that indicate these cells as: 1) an effective tool for monitoring the acute infection, 2) a discriminatory variable that may help determine the risk of nosocomial infection and 3) in a longer term, a treatment target that would restore the immunological abnormalities that occur in sepsis.

Genetic variability of innate immunity impacts human susceptibility to fungal diseases

Fungi are a major threat in immunocompromised patients. Despite presenting similar degrees of immunosuppression, not all individuals at-risk ultimately develop fungal diseases. The traditional view of immune suppression as a key risk factor for susceptibility to fungal infections needs to be accommodated within new conceptual advances on host immunity and its relationship to fungal disease. The critical role of the immune system emphasizes the contribution of host genetic polymorphisms to fungal disease susceptibility. This review highlights the present knowledge on innate immunity genetics that associates with susceptibility to fungal diseases.

Pattern recognition receptor expression is not impaired in patients with chronic mucocutanous candidiasis with or without autoimmune polyendocrinopathy candidiasis ectodermal dystrophy

Patients with chronic mucocutaneous candidiasis (CMC) have an unknown primary immune defect and are unable to clear infections with the yeast Candida. CMC includes patients with AIRE gene mutations who have autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), and patients without known mutations. CMC patients have dysregulated cytokine production, suggesting that defective expression of pattern recognition receptors (PRRs) may underlie disease pathogenesis. In 29 patients with CMC (13 with APECED) and controls, we assessed dendritic cell (DC) subsets and monocyte Toll-like receptor (TLR) expression in blood. We generated and stimulated monocyte-derived (mo)DCs with Candida albicans, TLR-2/6 ligand and lipopolysaccharide and assessed PRR mRNA expression by polymerase chain reaction [TLR-1-10, Dectin-1 and -2, spleen tyrosine kinase (Syk) and caspase recruitment domain (CARD) 9] in immature and mature moDCs. We demonstrate for the first time that CMC patients, with or without APECED, have normal blood levels of plasmocytoid and myeloid DCs and monocyte TLR-2/TLR-6 expression. We showed that in immature moDCs, expression levels of all PRRs involved in anti-Candida responses (TLR-1, -2, -4, -6, Dectin-1, Syk, CARD9) were comparable to controls, implying that defects in PRR expression are not responsible for the increased susceptibility to Candida infections seen in CMC patients. However, as opposed to healthy controls, both groups of CMC patients failed to down-regulate PRR mRNA expression in response to Candida, consistent with defective DC maturation, as we reported recently. Thus, impaired DC maturation and consequent altered regulation of PRR signalling pathways rather than defects in PRR expression may be responsible for inadequate Candida handling in CMC patients.

Immune profile of squamous metaplasia development in autoimmune regulator-deficient dry eye

PURPOSE

Squamous metaplasia of the ocular surface epithelium in severe Sjögren syndrome (SS) dry eye has been implicated to be associated with chronic engagement of immune-mediated inflammation. While the detailed immunopathological mechanism underlying keratinization of the ocular muco-epithelium in this setting remains unclear, mice deficient in the autoimmune regulator gene (Aire) demonstrate SS-like pathological changes in the exocrine organs and ocular surface including squamous metaplasia. Using this murine model, we sought to determine the specific immune events that predict squamous metaplasia of the cornea in Aire deficiency.

METHODS

Lissamine green staining, goblet cell density, and corneal small proline-rich protein 1B (SPRR1B) were compared in Aire-sufficient and -deficient mice at 4, 8, and 16 weeks of age. Corneal, limbal and conjunctival infiltration of CD4(+) and CD8(+) T cells as well as CD11c(+) and MHC class II (I-A(d+)) dendritic cells (DCs) were examined at the same time points. Ordinary least squares regression was used to model SPRR1B's relationship with lissamine green staining, goblet cell density, and immune cell infiltration.

RESULTS

Lissamine green staining was present in Aire-deficient mice by four weeks of age and increased over time. Compared to Aire-sufficient controls, conjunctival goblet cell density (GCD) decreased and corneal SPRR1B increased in Aire-deficient mice with significant differences noted at both 8 and 16 weeks. Immune-mediated CD4(+) T cell infiltration of the conjunctiva and limbus peaked at eight weeks and then decreased. In contrast, corneal T cell infiltration continued to increase over time, reaching a maximum cell number at 16 weeks. CD11c(+) myeloid-derived DCs were found in the conjunctiva and limbus at all time points. As the mice aged, there was a notable increase in corneal CD11c(+) cell counts. Interestingly, the dynamic of activated MHC class II(+) DCs was nearly identical to that of CD4(+) T cells, peaking first in the limbus at eight weeks with maximum infiltration of the cornea by 16 weeks. Regression analysis showed that squamous metaplasia biomarker, SPRR1B, is strongly related to the lissamine green staining of the ocular surface. Corneal infiltration of activated DCs was most prognostic of corneal SPRR1B expression while the presence of precursor DCs, activated DCs, and CD4(+) T cells in the limbus were also significant predictors of SPRR1B.

CONCLUSIONS

Aire-deficient mice represent a useful model to study Sjögren-like autoimmune-mediated ocular surface disease. Results of the current study suggest that squamous cell precursor protein, SPRR1B, provides an important readout to evaluate ocular surface damage and specific events related to immune-mediated inflammation. Results also define an appropriate time frame for interventional studies to develop more effective therapies for keratinizing ocular surface 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.