Malassezia specific IgE in head and neck dermatitis of eczema: A systematic review & meta-analysis.

Head and neck atopic dermatitis (HNAD) is a subtype of atopic dermatitis (AD), a common inflammatory skin condition with a distinctive clinical appearance. Malassezia spp., a predominant skin yeast, is considered to exacerbate HNAD. In this study, we investigate the prevalence of Malassezia-specific IgE among HNAD patients. A comprehensive search was performed for observational studies analysing the association between Malassezia-specific IgE and HNAD. This study was performed according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses 2020 checklist and quality was assessed via the Newcastle-Ottawa Quality Assessment Scale (NOS). Fourteen observational studies (840 patients) were included in the analysis. 58% of HNAD patients were male (95% CI: 45.2-69.7). Overall prevalence of Malassezia-specific IgE among HNAD patients was 79.3% (95% CI: 57.5-91.5). Prevalence of Malassezia-specific IgE among HNAD patients varied significantly between geographical regions (p = 0.0441), with 88% in non-Asian regions (95% CI: 61.06-97.17) and 54.73% in Asian regions (95% CI: 34.36-73.63). Malassezia-specific IgE prevalence among HNAD patients varied significantly among studies of higher and lower NOS quality score (p = 0.0386), with 95.42% in studies with NOS ≥7 (95% CI: 63.54-99.60) and 58.05% in studies with NOS <7 (95% CI: 41.44-73.01). Malassezia-specific IgE prevalence among HNAD patients did not vary significantly between more and less predominant Malassezia species (p = 0.1048). Malassezia spp. plays a crucial role in the pathogenesis of HNAD, and IgE anti-Malassezia antibodies appeared to be a common marker for HNAD. Understanding the pathophysiology of Malassezia in HNAD can help develop more targeted therapeutic approaches in managing AD.

[Diagnosis of allergen components in fungi and microbial communities: patient sensitization characteristics and main sensitizing proteins].

The human body, as a highly complex ecosystem, harbors diverse microbial communities, with major factors triggering allergic reactions encompassing the skin microbiome and fungi. The global diversity of fungi is estimated to range from approximately 600 000 to 1 million species, and theoretically, IgE-mediated sensitization may occur to any fungal species. As of now, the World Health Organization/IUIS official database records 113 fungal allergens originating from 30 different fungi species, covering 42 allergen families. Regarding the skin microbiome, 14 distinct Malassezia allergens have been identified, all derived from three different Malassezia fungi species--M. furfur, M. sympodialis, and M. globosa. The conditions of patients with these allergies are exceptionally complex. This article extensively discusses the latest research advancements and clinical applications related to skin microbiome and fungal allergies from the European Academy of Allergy and Clinical Immunology (EAACI) publication, "Molecular Allergology User's Guide 2.0". Additionally, it compiles information on the sources of fungal allergens, characteristics of allergen component protein families, clinical relevance, and management strategies, both domestically and internationally. The aim is to enhance the profound understanding of allergen components among relevant professionals. Through the application of advanced allergen component diagnostic techniques, the goal is to achieve precise diagnosis and treatment of fungal allergy patients and explore the mechanisms underlying fungal sensitization and pathogenesis, laying the foundation for studying the fungal allergen protein sensitization spectrum in the Chinese population.

Epidermal barrier impairment predisposes for excessive growth of the allergy-associated yeast Malassezia on murine skin.

BACKGROUND: The skin barrier is vital for protection against environmental threats including insults caused by skin-resident microbes. Dysregulation of this barrier is a hallmark of atopic dermatitis (AD) and ichthyosis, with variable consequences for host immune control of colonizing commensals and opportunistic pathogens. While Malassezia is the most abundant commensal fungus of the skin, little is known about the host control of this fungus in inflammatory skin diseases. METHODS: In this experimental study, MC903-treated mice were colonized with Malassezia spp. to assess the host-fungal interactions in atopic dermatitis. Additional murine models of AD and ichthyosis, including tape stripping, K5-Nrf2 overexpression and flaky tail mice, were employed to confirm and expand the findings. Skin fungal counts were enumerated. High parameter flow cytometry was used to characterize the antifungal response in the AD-like skin. Structural and functional alterations in the skin barrier were determined by histology and transcriptomics of bulk skin. Finally, differential expression of metabolic genes in Malassezia in atopic and control skin was quantified. RESULTS: Malassezia grows excessively in AD-like skin. Fungal overgrowth could, however, not be explained by the altered immune status of the atopic skin. Instead, we found that by upregulating key metabolic genes in the altered cutaneous niche, Malassezia acquired enhanced fitness to efficiently colonise the impaired skin barrier. CONCLUSIONS: This study provides evidence that structural and metabolic changes in the dysfunctional epidermal barrier environment provide increased accessibility and an altered lipid profile, to which the lipid-dependent yeast adapts for enhanced nutrient assimilation. Our findings reveal fundamental insights into the implication of the mycobiota in the pathogenesis of common skin barrier disorders.

Pilot study of dogs with suppurative and non-suppurative Malassezia otitis: A case series.

BACKGROUND: Rarely, Malassezia otitis presents as a painful, erosive otitis with an otic discharge containing Malassezia and neutrophils on cytology. There are no published reports of this type of suppurative Malassezia otitis (SMO). The role of Malassezia hypersensitivity in otitis is still unknown, and no association has been demonstrated with SMO. We compared Malassezia IgE levels, intradermal test and histology changes in SMO dogs with the more conventional Malassezia otitis (MO) presentation. RESULTS: Three dogs (case 1, case 2 and case 3) were diagnosed with SMO, one dog (case 4) was diagnosed with unilateral MO and unilateral SMO, and one dog (case 5) was diagnosed with MO. Only one case (case 4) with SMO/MO had a positive Intradermal Allergy Test (IDAT) and elevated IgE levels for Malassezia. Histopathology findings from SMO revealed: interface dermatitis (case 1 and 3), lymphocytic dermatitis (case 2) and chronic hyperplastic eosinophilic and lymphoplasmacytic dermatitis (case 4). Histopathology findings from MO showed perivascular dermatitis (case 4 and 5). All the cases were treated successfully. CONCLUSIONS: SMO presents with a distinct clinical phenotype in comparison with conventional MO. No consistent aetiology could be isolated. In these clinical cases it is possible that previous treatments could have influenced the results. More research is needed to understand the possible aetiologies and the pathogenesis of SMO.

Distribution of Malassezia species on the skin of patients with psoriasis.

INTRODUCTION: Malassezia species can induce the expression of interleukin-17 (IL-17), which plays an important role in the inflammatory and immune response in psoriasis (PS). The purpose of this study was to investigate the Malassezia species composition in patients with PS and healthy individuals and explore the role of Malassezia species in the pathogenesis of PS. MATERIALS AND METHODS: A total of 28 patients with PS and 10 age- and sex-matched healthy individuals participated in this study. Specimens collected from the lesional and non-lesional skin of patients with PS and the skin of healthy individuals were analyzed by using nested PCR. RESULTS: The relative abundance of Malassezia species was 84.96% in healthy subjects, more than twice that in patients with PS (P<0.01). M. restricta (43.09%) and M. globosa (41.38%) were the main Malassezia species in patients with PS followed by M. furfur (4.84%) and M. sympodialis (2.49%). M. sympodialis accounted for 18. 81% of the Malassezia species in healthy subjects, which was nearly eight times higher than in patients with PS (P<0.01). Further, M. furfur was detected both on lesional and non-lesional psoriatic skin, but it was not found on the skin of healthy individuals. CONCLUSIONS: The Malassezia species composition in patients with PS differed from that of healthy individuals. M. restricta and M. globosa were the main Malassezia species in patients with PS.

Malassezia spp. induce inflammatory cytokines and activate NLRP3 inflammasomes in phagocytes.

Malassezia spp. are common eukaryotic yeasts that colonize mammalian skin. Recently, the authors and others have observed that Malassezia globosa and Malassezia restricta can be found in the intestines in the context of certain diseases, including Crohn's disease and pancreatic cancer. In order to better understand the nature of innate inflammatory responses to these yeasts, inflammatory responses induced by M. restricta and M. globosa in mouse bone marrow-derived Mϕs (BMDM) and dendritic cells (BMDC) are evaluated. While Malassezia yeasts induce proinflammatory cytokine production from both Mϕs and dendritic cells, the levels of production from BMDC were more pronounced. Both M. restricta and M. globosa activated inflammatory cytokine production from BMDC in large part through Dectin2 and CARD9 signaling, although additional receptors appear to be involved in phagocytosis and activation of reactive oxygen production in response to the yeasts. Both M. restricta and M. globosa stimulate production of pro-IL-1ß as well as activation of the NLRP3 inflammasome. NLRP3 inflammasome activation by Malassezia fungi requires SYK signaling, potassium efflux and actin rearrangement. Together, the data further the understanding of the coordinated involvement of multiple innate immune receptors in recognizing Malassezia globosa and Malassezia restricta and orchestrating phagocyte inflammatory and antimicrobial responses.

Inflammasome-mediated Inflammation by Malassezia in human keratinocytes: A comparative analysis with different strains.

Malassezia species are associated with several common dermatologic conditions including pityriasis versicolor, seborrhoeic dermatitis, folliculitis, and atopic dermatitis and dandruff. However, its causal role remains to be established. We intended to explore the role of inflammasome activation in human keratinocytes in response to three different Malassezia species. We compared the different activation patterns of inflammasomes and the expression of pro-inflammatory cytokines and antimicrobial peptides by three different Malassezia species-M. restricta, M. globosa and M. sympodialis-in human keratinocytes. We found that different Malassezia species, especially M. restricta and M. globosa could induce nucleotide-binding oligomerisation domain, leucine-rich repeat and pyrin-domain-containing protein (NLRP)3-apoptosis-associated speck-like protein containing CARD (ASC) inflammasome activation and subsequent interleukin (IL)-1ß secretion in human keratinocytes. Malassezia species variably induced thymic stromal lymphopoietin, ß-defensin 2, and LL-37. IL-8 mRNA and IL-22 protein significantly increased in the M. sympodialis-treated group, and Chemokine C-C motif ligand (CCL)17 and CCL22 mRNA were increased in response to M. globosa- and M. restricta- treated keratinocytes, respectively. Our data show that various species of Malassezia promote variable inflammatory responses in keratinocytes by activating NLRP3 inflammasomes, pro-inflammatory cytokines and chemokines, and antimicrobial peptides.

A Novel Mycovirus Evokes Transcriptional Rewiring in the Fungus Malassezia and Stimulates Beta Interferon Production in Macrophages.

Mycoviruses infect fungi, and while most persist asymptomatically, there are examples of mycoviruses having both beneficial and detrimental effects on their host. Virus-infected Saccharomyces and Ustilago strains exhibit a killer phenotype conferring a growth advantage over uninfected strains and other competing yeast species, whereas hypovirus-infected Cryphonectria parasitica displays defects in growth, sporulation, and virulence. In this study, we identify a double-stranded RNA (dsRNA) mycovirus in five Malassezia species. Sequence analysis reveals it to be a totivirus with two dsRNA segments: a larger 4.5-kb segment with genes encoding components for viral replication and maintenance, and a smaller 1.4-kb segment encoding a novel protein. Furthermore, transcriptome sequencing (RNA-seq) of virus-infected versus virus-cured Malassezia sympodialis revealed an upregulation of dozens of ribosomal components in the cell, suggesting the virus modifies the transcriptional and translational landscapes of the cell. Given that Malassezia is the most abundant fungus on human skin, we assessed the impact of the mycovirus in a murine epicutaneous infection model. Although infection with virus-infected strains was not associated with an increased inflammatory response, we did observe enhanced skin colonization in one of two virus-infected M. sympodialis strains. Noteworthy, beta interferon expression was significantly upregulated in bone marrow-derived macrophages when challenged with virus-infected, compared to virus-cured, M. sympodialis, suggesting that the presence of the virus can induce an immunological response. Although many recent studies have illuminated how widespread mycoviruses are, there are relatively few in-depth studies about their impact on disease caused by the host fungus. We describe here a novel mycovirus in Malassezia and its possible implications in pathogenicity.IMPORTANCEMalassezia species represent the most common fungal inhabitant of the mammalian skin microbiome and are natural skin commensal flora. However, these fungi are also associated with a variety of clinical skin disorders. Recent studies have reported associations of Malassezia with Crohn's disease and pancreatic cancer, further implicating this fungal genus in inflammatory and neoplastic disease states. Because M. sympodialis has lost genes involved in RNA interference (RNAi), we hypothesized Malassezia could harbor dsRNA mycoviruses. Indeed, we identified a novel mycovirus of the totivirus family in several Malassezia species and characterized the MsMV1 mycovirus of M. sympodialis We found conditions that lead to curing of the virus and analyzed isogenic virus-infected/virus-cured strains to determine MsMV1 genetic and pathogenic impacts. MsMV1 induces a strong overexpression of transcription factors and ribosomal genes, while downregulating cellular metabolism. Moreover, MsMV1 induced a significantly higher level of beta interferon expression in cultured macrophages. This study sheds light on the mechanisms of pathogenicity of Malassezia, focusing on a previously unidentified novel mycovirus.

IgE sensitivity to Malassezia pachydermatis and mite allergens in dogs with atopic dermatitis.

In this study, dogs with atopic dermatitis were separated into non-food-induced atopic dermatitis (NFIAD) group (n = 15) and food-induced atopic dermatitis (FIAD) group (n = 37) based on an elimination diet test. IgE reactivity for crude Malassezia pachydermatis (M. pachydermatis) and house dust mites (HDM) allergen extracts was investigated in the two groups using fluorometric enzyme-linked immunosorbent assay (ELISA) and intradermal skin test (IDST). Nine (60%) of the 15 dogs in NFIAD group and 6 (16%) of the 37 dogs in FIAD group showed specific IgE for M. pachydermatis (Mann-Whitney U-test, P < 0.01). By immunoblotting analysis, the pooled serum samples from dogs with IgE for M. pachydermatis showed IgE reactivity for 50 kDa protein of M. pachydermatis. Twelve (80%) of the 15 dogs in NFIAD group and 8 (22%) of the 37 dogs in FIAD group showed specific IgE for HDM (Mann-Whitney U-test, P < 0.01). In addition, the dogs in NFIAD group significantly show a positive IDST to M. pachydermatis and HDM extracts compared with the dogs in FIAD group. The results suggest that dogs with NFIAD are at increased risk of becoming sensitized to the normal commensal organism M. pachydermatis compared with dogs with FIAD, perhaps co-sensitization occurred due to an HDM protease antigen's, Der f 1 and/or Der p 1, proteolytic activity related epidermal skin barrier defects. Treatment to limit skin colonization may thus be especially important in NFIAD.

The clinical impact of cross-reactions between allergens on allergic skin diseases.

PURPOSE OF REVIEW: The route of allergen sensing via the skin appears to influence the immune system towards mounting a type 2 response, especially in genetically predisposed individuals. Allergens recognized this way may derive from microbial, animal, food, or other plant sources and trigger atopic dermatitis. Allergens can be grouped into families depending on their structure and function, harboring significant structural and sequence similarities. Cross-reactivity between allergens is believed to arise as a consequence, and to underlie the development of further atopic diseases. RECENT FINDINGS: Especially for the plant allergens of the families of PR10-related proteins and profilins, immune cross-reactions have been described. Actual studies support that food and pollen allergens can aggravate skin lesions in patients suffering from atopic dermatitis. Further on, allergens derived from air-borne or skin-borne fungi belong to common allergen families and bear cross-reactivity potential. Cross-reactivity to human homologous proteins, so-called autoallergens, is discussed to contribute to the chronification of atopic dermatitis. SUMMARY: Due to high evolutionary conservation, allergic reactions can be triggered by highly homologous members of allergen families on the humoral as well as on the cellular level.

A Practical Approach to Recalcitrant Face and Neck Dermatitis in Atopic Dermatitis.

Face and neck dermatitis in the atopic dermatitis patient is a diagnostically challenging entity with broad differential diagnoses. Recent case reports reporting face and neck dermatitis in patients on dupilumab therapy have added further complexity to diagnosis and management. Herein, we discuss a broad diagnostic algorithm and practical management strategy for recalcitrant face and neck dermatitis in the atopic patient with an emphasis on face and neck dermatitis associated with dupilumab therapy. Our aim is to raise awareness about the probable entity of drug-associated face and neck dermatitis and share a practical management strategy that may also be applied broadly to atopic dermatitis patients presenting with face and neck dermatitis.

Extracellular Vesicles Released From the Skin Commensal Yeast Malassezia sympodialis Activate Human Primary Keratinocytes.

Extracellular vesicles (EVs) released from fungi have been shown to participate in inter-organismal communication and in cross-kingdom modulation of host defense. Malassezia species are the dominant commensal fungal members of the human skin microbiota. We have previously found that Malassezia sympodialis releases EVs. These EVs, designated MalaEx, carry M. sympodialis allergens and induce a different inflammatory cytokine response in peripheral blood mononuclear cells (PBMC) from patients with atopic dermatitis compared to healthy controls. In this study, we explored the host-microbe interaction between MalaEx and human keratinocytes with the hypothesis that MalaEx might be able to activate human keratinocytes to express the intercellular adhesion molecule-1 (ICAM-1, CD54). MalaEx were prepared from M. sympodialis (ATCC 42132) culture supernatants by a combination of centrifugation, filtration and serial ultracentrifugation. The MalaEx showed a size range of 70-580 nm with a mean of 154 nm using nanoparticle tracking analysis. MalaEx were found to induce a significant up-regulation of ICAM-1 expression on primary human keratinocytes isolated from human ex vivo skin (p = 0.026, n = 3), compared to the unstimulated keratinocytes. ICAM-1 is a counter ligand for the leukocyte integrins lymphocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1), of which induced expression on epithelial cells leads to the attraction of immune competent cells. Thus, the capacity of MalaEx to activate keratinocytes with an enhanced ICAM-1 expression indicates an important step in the cutaneous defense against M. sympodialis. How this modulation of host cells by a fungus is balanced between the commensal, pathogenic, or beneficial states on the skin in the interplay with the host needs to be further elucidated.

The pattern recognition receptors dectin-2, mincle, and FcRγ impact the dynamics of phagocytosis of Candida, Saccharomyces, Malassezia, and Mucor species.

Phagocytosis is a receptor-mediated process critical to innate immune clearance of pathogens. It proceeds in a regulated sequence of stages: (a) migration of phagocytes towards pathogens, (b) recognition of PAMPs and binding through PRRs, (c) engulfment and internalisation into phagosomes, (d) phagosome maturation, and (e) killing of pathogen or host cells. However, little is known about the role that individual receptors play in these discrete stages in the recognition of fungal cells. In a previous study, we found that dectin-2 deficiency impacted some but not all stages of macrophage-mediated phagocytosis of Candida glabrata. Because the C-type lectin receptor dectin-2 critically requires coupling to the FcRγ chain for signalling, we hypothesised that this coupling may be important for regulating phagocytosis of fungal cargo. We therefore examined how deficiency in FcRγ itself or two receptors to which it couples (dectin-2 and mincle) impacts phagocytosis of six fungal organisms representing three different fungal taxa. Our data show that deficiency in these proteins impairs murine bone marrow-derived macrophage migration, engulfment, and phagosome maturation, but not macrophage survival. Therefore, FcRγ engagement with selective C-type lectin receptors (CLRs) critically affects the spatio-temporal dynamics of fungal phagocytosis.

Human thioredoxin, a damage-associated molecular pattern and Malassezia-crossreactive autoallergen, modulates immune responses via the C-type lectin receptors Dectin-1 and Dectin-2.

Human thioredoxin (hTrx), which can be secreted from cells upon stress, functions in allergic skin inflammation as a T cell antigen due to homology and cross-reactivity with the fungal allergen Mala s13 of the skin-colonizing yeast Malassezia sympodialis. Recent studies have shown that cell wall polysaccharides of Malassezia are detected by the immune system via the C-type lectin receptors Dectin-1 and Dectin-2, which are expressed on myeloid cells. Therefore, this study aimed to investigate a putative interaction between Dectin-1, Dectin-2 and the allergens Mala s13 and hTrx. Stimulation of human monocyte-derived dendritic cells or macrophages with Mala s13 or hTrx resulted in remarkable secretion of IL-1ß and IL-23. Blocking experiments suggest that hTrx induces IL-23 by Dectin-1 binding and IL-1ß by binding to either Dectin-1 or Dectin-2. Regarding Mala s13, Dectin-1 appears to be involved in IL-1ß signaling. Interference of Syk kinase function was performed to investigate downstream signaling, which led to diminished hTrx responses. In our experiments, we observed rapid internalization of Mala s13 and hTrx upon cell contact and we were able to confirm direct interaction with Dectin-1 as well as Dectin-2 applying a fusion protein screening platform. We hypothesize that this cytokine response may result in a Th2/Th17-polarizing milieu, which may play a key role during the allergic sensitization in the skin, where allergen presentation to T cells is accompanied by microbial colonization and skin inflammation.

Malassezia interaction with a reconstructed human epidermis: Keratinocyte immune response.

The immediate immune response developed by the keratinocytes against Malassezia yeasts has been addressed yielding conflicting results. This study aims the assessment of cytokines and antimicrobial peptides gene expression elicited by M. sympodialis and M. furfur once in contact with a reconstructed human epidermis. A yeast suspension was prepared in RPMI 1640 medium (Sigma-Aldrich, St. Louis, MO) supplemented with Tween 60 and oleic acid to obtain approximately 1 × 106 cells in a volume of 100 µL. Clinical isolates of M. sympodialis (from pityriasis versicolor) and M. furfur (from seborrhoeic dermatitis) were inoculated, separately, onto a reconstructed human epidermis. A distinct expression pattern was found between the two tested species, with a tendency for overexpression of pro-inflammatory cytokines very soon after infection, whereas no significant expression or gene downregulation was often noticed following 24 and 48 h of incubation. A possible Malassezia species-dependent immune response pattern is highlighted.

The role of the skin microbiota in acne pathophysiology.

BACKGROUND: The role of skin microbiota in acne remains to be fully elucidated. Initial culture-based investigations were hampered by growth rate and selective media bias. Even with less biased genomic methods, sampling, lysis and methodology, the task of describing acne pathophysiology remains challenging. Acne occurs in sites dominated by Cutibacterium acnes (formerly Propionibacterium acnes) and Malassezia species, both of which can function either as commensal or pathogen. OBJECTIVES: This article aims to review the current state of the art of the microbiome and acne. METHODS: The literature regarding the microbiome and acne was reviewed. RESULTS: It remains unclear whether there is a quantitative difference in microbial community distribution, making it challenging to understand any community shift from commensal to pathogenic nature. It is plausible that acne involves (i) change in the distribution of species/strains, (ii) stable distribution with pathogenic alteration in response to internal (intermicrobe) or external stimuli (host physiology or environmental) or (iii) a combination of these factors. CONCLUSIONS: Understanding physiological changes in bacterial species and strains will be required to define their specific roles, and identify any potential intervention points, in acne pathogenesis and treatment. It will also be necessary to determine whether any fungal species are involved, and establish whether they play a significant role. Further investigation using robust, modern analytic tools in longitudinal studies with a large number of participants, may make it possible to determine whether the microbiota plays a causal role, is primarily involved in exacerbation, or is merely a bystander. It is likely that the final outcome will show that acne is the result of complex microbe-microbe and community-host interplay.

Mechanisms of microbial pathogenesis and the role of the skin microbiome in psoriasis: A review.

The pathogenesis of psoriasis may involve a breakdown of immune tolerance to cutaneous microorganisms. Psoriasis is associated with a higher incidence of Crohn disease and periodontitis, two diseases involving impaired tolerance and abnormal immune activation in response to intestinal and oral microbiota, respectively. In addition, guttate and chronic plaque psoriasis are associated with Streptococcus pyogenes colonization. The aim of this review is to characterize the microorganisms implicated in psoriasis by examining results of major association studies and possible mechanisms of pathogenesis. Although studies show relative increases in Streptococcus and Staphylococcus and decreases in Malassezia and Cutibacterium, they differ in methods of sampling and methods of microbial analysis. As such, no definitive associations between microbes and psoriasis have been found to date. It also remains unclear if changes in the microbiomal composition have a causal association with psoriasis or are simply a consequence of the inflammatory microenvironment. Techniques enabling strain-level analysis rather than species-level analysis of the skin microbiome are likely necessary to determine microbiomal signatures of psoriasis. Future investigations may lead to new diagnostic tests and novel treatments, such as probiotics or bacterial transplantation.

The Skin Commensal Yeast Malassezia Triggers a Type 17 Response that Coordinates Anti-fungal Immunity and Exacerbates Skin Inflammation.

Commensal fungi of the mammalian skin, such as those of the genus Malassezia, are associated with atopic dermatitis and other common inflammatory skin disorders. Understanding of the causative relationship between fungal commensalism and disease manifestation remains incomplete. By developing a murine epicutaneous infection model, we found Malassezia spp. selectively induce IL-17 and related cytokines. This response is key in preventing fungal overgrowth on the skin, as disruption of the IL-23-IL-17 axis compromises Malassezia-specific cutaneous immunity. Under conditions of impaired skin integrity, mimicking a hallmark of atopic dermatitis, the presence of Malassezia dramatically aggravates cutaneous inflammation, which again was IL-23 and IL-17 dependent. Consistently, we found a CCR6+ Th17 subset of memory T cells to be Malassezia specific in both healthy individuals and atopic dermatitis patients, whereby the latter showed enhanced frequency of these cells. Thus, the Malassezia-induced type 17 response is pivotal in orchestrating antifungal immunity and in actively promoting skin inflammation.

Extracellular vesicles derived from Malassezia furfur stimulate IL-6 production in keratinocytes as demonstrated in in vitro and in vivo models.

BACKGROUND: Malassezia is one of the commensal microorganisms colonized on human skin and has been shown to be related to several inflammatory cutaneous disorders. Previous studies indicated that Malassezia. sympodialis (M. sympodialis) can produce extracellular vesicles, however, the immunoregulatory function of Malassezia extracellular vesicles on keratinocytes has not been studied. OBJECTIVE: To investigate the extracellular vesicular production capability of Malassezia. furfur (M. furfur) and examine their immunoregulatory effects both in vitro and in vivo. METHODS: Extracellular vesicles derived from M. furfur were isolated by sequential ultracentrifugation procedure. Their structure and diameter were determined by negative stain TEM and NTA, respectively. Confocal microscopy was used to visualize the internalization of these nanoparticles into HaCaT cells and mice epidermal keratinocytes. The expressions of inflammatory cytokines were screened using PCR Array assay and validated in vitro by qPCR and ELISA assays. In vivo cytokine production was measured by the IHC method. The role of NF-κB in such process was evaluated in HaCaT cells by western blot assay. RESULTS: Our results showed that M. furfur produced ovoid-shaped nanoparticles, which could be then internalized into HaCaT cells, as well as mice epidermal keratinocytes. IL-6 expression was significantly enhanced in response to extracellular vesicular stimulation both in vitro and in vivo, in which process the activation of NF-κB was involved. CONCLUSION: M. furfur has the ability to release extracellular vesicles, which can be internalized into keratinocytes and promote the production of IL-6 with the involvement of NF-κB dependent pathway. Such findings reveal some important new insights into Malassezia pathogenesis and therapy.

Contribution of Malassezia spp. to the development of atopic dermatitis.

The prevalence of atopic dermatitis (AD) has been increasing. Whereas AD symptoms are obvious and easy to recognise, the etiopathogenesis remains not fully elucidated. Recently, the role of microorganisms and their impact on the immunology of AD have been discussed. In this review, we summarise a possible role of Malassezia in the development and persistence of eczema in patients with atopic eczema/dermatitis syndrome. A high proportion of AD patients present with a positive reaction to Malassezia allergens. Several possible pathogenic mechanisms enable Malassezia to trigger the development of AD. Malassezia spp. may release more allergens in a less acidic (pH <6), typical for AD, environment. The similarity between fungal thioredoxin and human proteins causes T-cell cross-reactivity. TLR-mediated mechanisms are involved in host response against Malassezia spp. An interaction between Malassezia spp. and keratinocytes alters the profile of cytokine release, and what is more, yeast cells can survive when absorbed by keratinocytes. Dendritic cells of AD patients induced by Malassezia are less susceptible to lysis mediated by NK cells which exerts a pro-inflammatory effect. Despite the evidence that Malassezia spp. contribute to the development of AD, the pathogenetic mechanisms and relationship between Malassezia and immune defense remain partly unexplained and require further research.