The immune and microbial homeostasis determines the Candida-mast cells cross-talk in celiac disease.

Celiac disease (CD) is an autoimmune enteropathy resulting from an interaction between diet, genome, and immunity. Although many patients respond to a gluten-free diet, in a substantive number of individuals, the intestinal injury persists. Thus, other factors might amplify the ongoing inflammation. Candida albicans is a commensal fungus that is well adapted to the intestinal life. However, specific conditions increase Candida pathogenicity. The hypothesis that Candida may be a trigger in CD has been proposed after the observation of similarity between a fungal wall component and two CD-related gliadin T-cell epitopes. However, despite being implicated in intestinal disorders, Candida may also protect against immune pathologies highlighting a more intriguing role in the gut. Herein, we postulated that a state of chronic inflammation associated with microbial dysbiosis and leaky gut are favorable conditions that promote C. albicans pathogenicity eventually contributing to CD pathology via a mast cells (MC)-IL-9 axis. However, the restoration of immune and microbial homeostasis promotes a beneficial C. albicans-MC cross-talk favoring the attenuation of CD pathology to alleviate CD pathology and symptoms.

Complement receptor 3-dependent engagement by Candida glabrata ß-glucan modulates dendritic cells to induce regulatory T-cell expansion.

Candida glabrata is an important pathogen causing invasive infection associated with a high mortality rate. One mechanism that causes the failure of Candida eradication is an increase in regulatory T cells (Treg), which play a major role in immune suppression and promoting Candida pathogenicity. To date, how C. glabrata induces a Treg response remains unclear. Dendritic cells (DCs) recognition of fungi provides the fundamental signal determining the fate of the T-cell response. This study investigated the interplay between C. glabrata and DCs and its effect on Treg induction. We found that C. glabrata ß-glucan was a major component that interacted with DCs and consequently mediated the Treg response. Blocking the binding of C. glabrata ß-glucan to dectin-1 and complement receptor 3 (CR3) showed that CR3 activation in DCs was crucial for the induction of Treg. Furthermore, a ligand-receptor binding assay showed the preferential binding of C. glabrata ß-glucan to CR3. Our data suggest that C. glabrata ß-glucan potentially mediates the Treg response, probably through CR3-dependent activation in DCs. This study contributes new insights into immune modulation by C. glabrata that may lead to a better design of novel immunotherapeutic strategies for invasive C. glabrata infection.

Hyphal Als proteins act as CR3 ligands to promote immune responses against Candida albicans.

Patients with decreased levels of CD18 (ß2 integrins) suffer from life-threatening bacterial and fungal infections. CD11b, the α subunit of integrin CR3 (CD11b/CD18, αMß2), is essential for mice to fight against systemic Candida albicans infections. Live elongating C. albicans activates CR3 in immune cells. However, the hyphal ligands that activate CR3 are not well defined. Here, we discovered that the C. albicans Als family proteins are recognized by the I domain of CD11b in macrophages. This recognition synergizes with the ß-glucan-bound lectin-like domain to activate CR3, thereby promoting Syk signaling and inflammasome activation. Dectin-2 activation serves as the "outside-in signaling" for CR3 activation at the entry site of incompletely sealed phagosomes, where a thick cuff of F-actin forms to strengthen the local interaction. In vitro, CD18 partially contributes to IL-1ß release from dendritic cells induced by purified hyphal Als3. In vivo, Als3 is vital for C. albicans clearance in mouse kidneys. These findings uncover a novel family of ligands for the CR3 I domain that promotes fungal clearance.

A chemically induced attenuated strain of Candida albicans generates robust protective immune responses and prevents systemic candidiasis development.

Despite current antifungal therapy, invasive candidiasis causes >40% mortality in immunocompromised individuals. Therefore, developing an antifungal vaccine is a priority. Here, we could for the first time successfully attenuate the virulence of Candida albicans by treating it with a fungistatic dosage of EDTA and demonstrate it to be a potential live whole cell vaccine by using murine models of systemic candidiasis. EDTA inhibited the growth and biofilm formation of C. albicans. RNA-seq analyses of EDTA-treated cells (CAET) revealed that genes mostly involved in metal homeostasis and ribosome biogenesis were up- and down-regulated, respectively. Consequently, a bulky cell wall with elevated levels of mannan and ß-glucan, and reduced levels of total monosomes and polysomes were observed. CAET was eliminated faster than the untreated strain (Ca) as found by differential fungal burden in the vital organs of the mice. Higher monocytes, granulocytes, and platelet counts were detected in Ca- vs CAET-challenged mice. While hyper-inflammation and immunosuppression caused the killing of Ca-challenged mice, a critical balance of pro- and anti-inflammatory cytokines-mediated immune responses are the likely reasons for the protective immunity in CAET-infected mice.

Tryptophan metabolites relieve intestinal Candida albicans infection by altering the gut microbiota to reduce IL-22 release from group 3 innate lymphoid cells of the colon lamina propria.

Invasive candidiasis may be caused by Candida albicans (C. albicans) colonization of the intestinal tract. Preventing intestinal damage caused by Candida albicans infection and protecting intestinal barrier function have become a critical issue. Integrated analyses of the microbiome with metabolome revealed a remarkable shift of the gut microbiota and tryptophan metabolites, kynurenic acid (KynA), and indolacrylic acid (IA) in mice infected with C. albicans. The transcriptome sequencing indicated that differentially expressed genes were significantly associated with innate immune responses and inflammatory responses. The results of this study suggest that KynA and IA (KI) can alleviate intestinal damage caused by Candida albicans infection in mice by reducing intestinal permeability, increasing intestinal firmness, alleviating intestinal inflammation, and reducing the secretion of interleukin-22 (IL-22) in the 3 groups of colon innate lymphoid cells (ILC3). We performed a fecal microbiota transplantation (FMT) experiment and found that the intestinal barrier function, inflammation, and IL-22 secretion of ILC3 in the colon lamina propria of the recipient mice subjected to C. albicans infection and KI treatment were consistent with the trends of the donor mice. Our results suggest that tryptophan metabolites may directly regulate colon lamina ILC3 to promote intestinal resistance to C. albicans invasion, or indirectly regulate the ILC3 secretion of IL-22 to play a protective role in the intestinal barrier by affecting intestinal microorganisms, which may become a potential target for alleviating intestine borne C. albicans infection.

Immune response to colonization of Candida albicans in mice treated with Cefoperazone.

Candida species are a normal human flora in humans' digestive and reproductive systems, oral cavity, skin, and mucosal surfaces. This study aimed to detect the immunological role of Candida infection by using some immunological markers. The results of levels in serum showed high concentrations of IgA (56.20 ± 12 pg/ml,29.55 ± 4.5 pg/ml respectively) and IgG (12.05 ± 3.218 pg/ml, 3.836 ± 1.23 pg/ml respectively) in mice infected with C. albicans and mice treated with Cefoperazone and infected with Candida with significant differences (P value < 0.05). The results showed high serum levels of IL-17(191.5 ± 42.81 pg/ml) and TLR2(7.651 ± 1.5 pg/ml) in group mice infected with C. albicans compared with negative control and group mice treated with Cefoperazone. Also, high levels of IL-17 (91.33 ± 4.816 pg/ml) and TLR2 (2.630 ± 0.5 pg/ml) in group mice treated with Cefoperazone and infected with Candida compared with negative control and group mice treated with Cefoperazone (P value < 0.05). The results of antibodies and immunological markers in the intestine showed high levels of IgA and IgG in mice infected with C.albicans (55.7 ± 4.9 pg/ml, 18.19 ± 0.63 pg/ml respectively).Also,IgA and IgG in mice treated with Cefoperazone and infected with Candida were high level (43.04 ± 2.1 pg/ml, 2.927 ± 0.2 pg/ml respectively) in mice infected with C. albicans with significant differences (P value < 0.05). The results levels of IL-17 and TLR2 were increased in mice infected with C. albicans (191.5 ± 42.81 pg/ml, 7.651 ± 1.5 pg/ml respectively) and mice treated with Cefoperazone and infected with Candida (91.33 ± 4.816 pg/ml,2.630 ± 0.5 pg/ml respectively) with significant differences (P < 0.05). In conclusion, this study demonstrated that cefoperazone treatment and infection by Candida albicans changed the microbiome components in the gut and finally can change host immune responses. It was observed that elevated levels of the antibodies production (IgA and IgG) and immunological markers (IL-17, and TLR2) in serum and the gut.

Identification of the Most Immunoreactive Antigens of Candida auris to IgGs from Systemic Infections in Mice.

The delay in making a correct diagnosis of Candida auris causes concern in the healthcare system setting, and immunoproteomics studies are important to identify immunoreactive proteins for new diagnostic strategies. In this study, immunocompetent murine systemic infections caused by non-aggregative and aggregative phenotypes of C. auris and by Candida albicans and Candida haemulonii were carried out, and the obtained sera were used to study their immunoreactivity against C. auris proteins. The results showed higher virulence, in terms of infection signs, weight loss, and histopathological damage, of the non-aggregative isolate. Moreover, C. auris was less virulent than C. albicans but more than C. haemulonii. Regarding the immunoproteomics study, 13 spots recognized by sera from mice infected with both C. auris phenotypes and analyzed by mass spectrometry corresponded to enolase, phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate mutase. These four proteins were also recognized by sera obtained from human patients with disseminated C. auris infection but not by sera obtained from mice infected with C. albicans or Aspergillus fumigatus. Spot identification data are available via ProteomeXchange with the identifier PXD049077. In conclusion, this study showed that the identified proteins could be potential candidates to be studied as new diagnostic or even therapeutic targets for C. auris.

Candida albicans increases the aerobic glycolysis and activates MAPK-dependent inflammatory response of liver sinusoidal endothelial cells.

The liver, and more specifically, the liver sinusoidal endothelial cells, constitute the beginning of one of the most important responses for the elimination of hematogenously disseminated Candida albicans. Therefore, we aimed to study the mechanisms involved in the interaction between these cells and C. albicans. Transcriptomics-based analysis showed an increase in the expression of genes related to the immune response (including receptors, cytokines, and adhesion molecules), as well as to aerobic glycolysis. Further in vitro analyses showed that IL-6 production in response to C. albicans is controlled by MyD88- and SYK-pathways, suggesting an involvement of Toll-like and C-type lectin receptors and the subsequent activation of the MAP-kinases and c-Fos/AP-1 transcription factor. In addition, liver sinusoidal endothelial cells undergo metabolic reprogramming towards aerobic glycolysis induced by C. albicans, as confirmed by the increased Extracellular Acidification Rate and the overexpression of enolase (Eno2), hexonikase (Hk2) and glucose transporter 1 (Slc2a1). In conclusion, these results indicate that the hepatic endothelium responds to C. albicans by increasing aerobic glycolysis and promoting an inflammatory environment.

FAM21 is critical for TLR2/CLEC4E-mediated dendritic cell function against Candida albicans.

FAM21 (family with sequence similarity 21) is a component of the Wiskott-Aldrich syndrome protein and SCAR homologue (WASH) protein complex that mediates actin polymerization at endosomal membranes to facilitate sorting of cargo-containing vesicles out of endosomes. To study the function of FAM21 in vivo, we generated conditional knockout (cKO) mice in the C57BL/6 background in which FAM21 was specifically knocked out of CD11c-positive dendritic cells. BMDCs from those mice displayed enlarged early endosomes, and altered cell migration and morphology relative to WT cells. FAM21-cKO cells were less competent in phagocytosis and protein antigen presentation in vitro, though peptide antigen presentation was not affected. More importantly, we identified the TLR2/CLEC4E signaling pathway as being down-regulated in FAM21-cKO BMDCs when challenged with its specific ligand Candida albicans Moreover, FAM21-cKO mice were more susceptible to C. albicans infection than WT mice. Reconstitution of WT BMDCs in FAM21-cKO mice rescued them from lethal C. albicans infection. Thus, our study highlights the importance of FAM21 in a host immune response against a significant pathogen.

Interactions of Candida tropicalis pH-related antigen 1 with complement proteins C3, C3b, factor-H, C4BP and complement evasion.

Candida, as a part of the human microbiota, can cause opportunistic infections that are either localised or systemic candidiasis. Emerging resistance to the standard antifungal drugs is associated with increased mortality rate due to invasive Candida infections, particularly in immunocompromised patients. While there are several species of Candida, an increasing number of Candida tropicalis isolates have been recently reported from patients with invasive candidiasis or inflammatory bowel diseases. In order to establish infections, C. tropicalis has to adopt several strategies to escape the host immune attack. Understanding the immune evasion strategies is of great importance as these can be exploited as novel therapeutic targets. C. albicans pH-related antigen 1 (CaPra1), a surface bound and secretory protein, has been found to interact strongly with the immune system and help in complement evasion. However, the role of C. tropicalis Pra1 (CtPra1) and its interaction with the complement is not studied yet. Thus, we characterised how pH-related antigen 1 of C. tropicalis (CtPra1) interacts with some of the key complement proteins of the innate immune system. CtPra1 was recombinantly produced using a Kluyveromyces lactis yeast expression system. Recombinant CtPra1, was found to bind human C3 and C3b, central molecules of the complement pathways that are important components of the innate immune system. It was also found to bind human complement regulatory proteins factor-H and C4b-binding protein (C4BP). CtPra1-factor-H and CtPra1-C4BP interactions were found to be ionic in nature as the binding intensity affected by high sodium chloride concentrations. CtPra1 inhibited functional complement activation with different effects on classical (∼20 %), lectin (∼25 %) and alternative (∼30 %) pathways. qPCR experiments using C. tropicalis clinical isolates (oral, blood and peritoneal fluid) revealed relatively higher levels of expression of CtPra1 gene when compared to the reference strain. Native CtPra1 was found to be expressed both as membrane-bound and secretory forms in the clinical isolates. Thus, C. tropicalis appears to be a master of immune evasion by using Pra1 protein. Further investigation using in-vivo models will help ascertain if these proteins can be novel therapeutic targets.

Measurements of Treg Cell Induction by Candida albicans DNA Using Flow Cytometry.

Microbiota and their metabolites in the human gut regulate a variety of immune cells including regulatory T cells (Treg cells) and cytokine production. The T helper 17 (Th17)/Treg ratio biomarker (Th17/Treg), for example, has been linked to the development and progression of certain inflammatory diseases, insulin resistance, and systemic lupus erythematosus (SLE). Candida albicans is an opportunistic fungal pathogen that also colonizes the gut. T cell reactivity through T helper cells play critical roles in fungal clearance by the host through the secretion of proinflammatory cytokines. While these cytokines are mainly produced by the Th1 and Th17 subsets of T cells, another subset of T cells, the Treg cells, are also induced by antigenic ligands from pathogens that inhibit the responses of other effector T cells during the inflammation. The antigenic ligands for Treg induction have been found to include microbial cell wall polysaccharides (PSA), metabolites like short chain fatty acids (SCFA), or even microbial DNA.

Fungal sensing enhances neutrophil metabolic fitness by regulating antifungal Glut1 activity.

Combating fungal pathogens poses metabolic challenges for neutrophils, key innate cells in anti-Candida albicans immunity, yet how host-pathogen interactions cause remodeling of the neutrophil metabolism is unclear. We show that neutrophils mediate renal immunity to disseminated candidiasis by upregulating glucose uptake via selective expression of glucose transporter 1 (Glut1). Mechanistically, dectin-1-mediated recognition of ß-glucan leads to activation of PKCδ, which triggers phosphorylation, localization, and early glucose transport by a pool of pre-formed Glut1 in neutrophils. These events are followed by increased Glut1 gene transcription, leading to more sustained Glut1 accumulation, which is also dependent on the ß-glucan/dectin-1/CARD9 axis. Card9-deficient neutrophils show diminished glucose incorporation in candidiasis. Neutrophil-specific Glut1-ablated mice exhibit increased mortality in candidiasis caused by compromised neutrophil phagocytosis, reactive oxygen species (ROS), and neutrophil extracellular trap (NET) formation. In human neutrophils, ß-glucan triggers metabolic remodeling and enhances candidacidal function. Our data show that the host-pathogen interface increases glycolytic activity in neutrophils by regulating Glut1 expression, localization, and function.

TLR Signaling Rescues Fungicidal Activity in Syk-Deficient Neutrophils.

An impaired neutrophil response to pathogenic fungi puts patients at risk for fungal infections with a high risk of morbidity and mortality. Acquired neutrophil dysfunction in the setting of iatrogenic immune modulators can include the inhibition of critical kinases such as spleen tyrosine kinase (Syk). In this study, we used an established system of conditionally immortalized mouse neutrophil progenitors to investigate the ability to augment Syk-deficient neutrophil function against Candida albicans with TLR agonist signaling. LPS, a known immunomodulatory molecule derived from Gram-negative bacteria, was capable of rescuing effector functions of Syk-deficient neutrophils, which are known to have poor fungicidal activity against Candida species. LPS priming of Syk-deficient mouse neutrophils demonstrates partial rescue of fungicidal activity, including phagocytosis, degranulation, and neutrophil swarming, but not reactive oxygen species production against C. albicans, in part due to c-Fos activation. Similarly, LPS priming of human neutrophils rescues fungicidal activity in the presence of pharmacologic inhibition of Syk and Bruton's tyrosine kinase (Btk), both critical kinases in the innate immune response to fungi. In vivo, neutropenic mice were reconstituted with wild-type or Syk-deficient neutrophils and challenged i.p. with C. albicans. In this model, LPS improved wild-type neutrophil homing to the fungal challenge, although Syk-deficient neutrophils did not persist in vivo, speaking to its crucial role on in vivo persistence. Taken together, we identify TLR signaling as an alternate activation pathway capable of partially restoring neutrophil effector function against Candida in a Syk-independent manner.

IL-33 Coordinates Innate Defense to Systemic Candida albicans Infection by Regulating IL-23 and IL-10 in an Opposite Way.

Invasive candidiasis has high mortality rates in immunocompromised patients, causing serious health problems. In mouse models, innate immunity protects the host by rapidly mobilizing a variety of resistance and tolerance mechanisms to systemic Candida albicans infection. We have previously demonstrated that exogenous IL-33 regulates multiple steps of innate immunity involving resistance and tolerance processes. In this study, we systematically analyzed the in vivo functions of endogenous IL-33 using Il33 -/- mice and in vitro immune cell culture. Tubular epithelial cells mainly secreted IL-33 in response to systemic C. albicans infection. Il33 -/- mice showed increased mortality and morbidity, which were due to impaired fungal clearance. IL-33 initiated an innate defense mechanism by costimulating dendritic cells to produce IL-23 after systemic C. albicans infection, which in turn promoted the phagocytosis of neutrophils through secretion of GM-CSF by NK cells. The susceptibility of Il33 -/- mice was also associated with increased levels of IL-10, and neutralization of IL-10 resulted in enhanced fungal clearance in Il33 -/- mice. However, depletion of IL-10 overrode the effect of IL-33 on fungal clearance. In Il10 -/- mouse kidneys, MHC class II+F4/80+ macrophages were massively differentiated after C. albicans infection, and these cells were superior to MHC class II-F4/80+ macrophages that were preferentially differentiated in wild-type mouse kidneys in killing of extracellular hyphal C. albicans Taken together, our results identify IL-33 as critical early regulator controlling a serial downstream signaling events of innate defense to C. albicans infection.

DOCK2 regulates antifungal immunity by regulating RAC GTPase activity.

Fungal infections cause ~1.5 million deaths each year worldwide, and the mortality rate of disseminated candidiasis currently exceeds that of breast cancer and malaria. The major reasons for the high mortality of candidiasis are the limited number of antifungal drugs and the emergence of drug-resistant species. Therefore, a better understanding of antifungal host defense mechanisms is crucial for the development of effective preventive and therapeutic strategies. Here, we report that DOCK2 (dedicator of cytokinesis 2) promotes indispensable antifungal innate immune signaling and proinflammatory gene expression in macrophages. DOCK2-deficient macrophages exhibit decreased RAC GTPase (Rac family small GTPase) activation and ROS (reactive oxygen species) production, which in turn attenuates the killing of intracellular fungi and the activation of downstream signaling pathways. Mechanistically, after fungal stimulation, activated SYK (spleen-associated tyrosine kinase) phosphorylates DOCK2 at tyrosine 985 and 1405, which promotes the recruitment and activation of RAC GTPases and then increases ROS production and downstream signaling activation. Importantly, nanoparticle-mediated delivery of in vitro transcribed (IVT) Rac1 mRNA promotes the activity of Rac1 and helps to eliminate fungal infection in vivo. Taken together, this study not only identifies a critical role of DOCK2 in antifungal immunity via regulation of RAC GTPase activity but also provides proof of concept for the treatment of invasive fungal infections by using IVT mRNA.

Control of ß-glucan exposure by the endo-1,3-glucanase Eng1 in Candida albicans modulates virulence.

Candida albicans is a major opportunistic pathogen of humans. It can grow as morphologically distinct yeast, pseudohyphae and hyphae, and the ability to switch reversibly among different forms is critical for its virulence. The relationship between morphogenesis and innate immune recognition is not quite clear. Dectin-1 is a major C-type lectin receptor that recognizes ß-glucan in the fungal cell wall. C. albicans ß-glucan is usually masked by the outer mannan layer of the cell wall. Whether and how ß-glucan masking is differentially regulated during hyphal morphogenesis is not fully understood. Here we show that the endo-1,3-glucanase Eng1 is differentially expressed in yeast, and together with Yeast Wall Protein 1 (Ywp1), regulates ß-glucan exposure and Dectin-1-dependent immune activation of macrophage by yeast cells. ENG1 deletion results in enhanced Dectin-1 binding at the septa of yeast cells; while eng1 ywp1 yeast cells show strong overall Dectin-1 binding similar to hyphae of wild-type and eng1 mutants. Correlatively, hyphae of wild-type and eng1 induced similar levels of cytokines in macrophage. ENG1 expression and Eng1-mediated ß-glucan trimming are also regulated by antifungal drugs, lactate and N-acetylglucosamine. Deletion of ENG1 modulates virulence in the mouse model of hematogenously disseminated candidiasis in a Dectin-1-dependent manner. The eng1 mutant exhibited attenuated lethality in male mice, but enhanced lethality in female mice, which was associated with a stronger renal immune response and lower fungal burden. Thus, Eng1-regulated ß-glucan exposure in yeast cells modulates the balance between immune protection and immunopathogenesis during disseminated candidiasis.

Study on the mechanism of Yupingfeng powder in the treatment of immunosuppression based on UPLC⁃QTOF⁃MS, network pharmacology and molecular biology verification.

AIMS: The current study aims to investigate the effect of Yupingfeng (YPF) powder on immunosuppression, and explore the possible mechanisms. MAIN METHODS: Firstly, the monomer components of YPF powder were analyzed by UPLC-QTOF-MS combined with UNIFI automatic analysis platform, then the mechanism of YPF on immunosuppressive treatment was investigated using network pharmacological method, and finally the prediction was verified in a Candida albicans (Can)-induced immunosuppressive BALB/c mouse model. KEY FINDINGS: 98 monomer compounds in YPF were obtained. Through virtual analysis and screening on the oral utilization and drug likeness properties of the components, 47 effective components were got. 9 core targets obtained were enriched in IL-17 signaling pathway. In the mouse model, YPF could reduce the number of Can and alleviate Can-induced inflammation in the kidney effectively, upregulate Can-induced low proportion of CD4+/CD8+ of splenic lymphocytes, and increase Can-induced low activity of IL-17 pathway. SIGNIFICANCE: These results demonstrate that YPF could improve the immunity of Can-induced immunosuppression in BALB/c mice through upregulating the activity of IL-17 pathway.

Interactions of Both Pathogenic and Nonpathogenic CUG Clade Candida Species with Macrophages Share a Conserved Transcriptional Landscape.

Candida species are a leading cause of opportunistic, hospital-associated bloodstream infections with high mortality rates, typically in immunocompromised patients. Several species, including Candida albicans, the most prevalent cause of infection, belong to the monophyletic CUG clade of yeasts. Innate immune cells such as macrophages are crucial for controlling infection, and C. albicans responds to phagocytosis by a coordinated induction of pathways involved in catabolism of nonglucose carbon sources, termed alternative carbon metabolism, which together are essential for virulence. However, the interactions of other CUG clade species with macrophages have not been characterized. Here, we analyzed transcriptional responses to macrophage phagocytosis by six Candida species across a range of virulence and clinical importance. We define a core induced response common to pathogenic and nonpathogenic species alike, heavily weighted to alternative carbon metabolism. One prominent pathogen, Candida parapsilosis, showed species-specific expansion of phagocytosis-responsive genes, particularly metabolite transporters. C. albicans and Candida tropicalis, the other prominent pathogens, also had species-specific responses, but these were largely comprised of functionally uncharacterized genes. Transcriptional analysis of macrophages also demonstrated highly correlated proinflammatory transcriptional responses to different Candida species that were largely independent of fungal viability, suggesting that this response is driven by recognition of conserved cell wall components. This study significantly broadens our understanding of host interactions in CUG clade species, demonstrating that although metabolic plasticity is crucial for virulence in Candida, it alone is not sufficient to confer pathogenicity. Instead, we identify sets of mostly uncharacterized genes that may explain the evolution of pathogenicity. IMPORTANCE Candidiasis is a major fungal infection by Candida species, causing life-threatening invasive disease in immunocompromised patients. C. albicans, which is adapted to commensalism of human mucosae, is the most common cause. While several other species cause infection, most are less prevalent or less virulent. As innate immune cells are the primary defense against Candida infection, we compared the transcriptional responses of C. albicans and related species to phagocytosis by macrophages, to understand the basis of variation in pathogenesis. This response, including the metabolic remodeling required for virulence in C. albicans, was strikingly conserved across the virulence spectrum. Macrophage responses to different species were also highly similar. This study indicates that important elements of host-pathogen interactions in C. albicans are not driven by adaptation to the mammalian host and improves our understanding of pathogenicity in opportunistic fungal species that are understudied but collectively impose a significant threat of their own.

B Cell Recognition of Candida albicans Hyphae via TLR 2 Promotes IgG1 and IL-6 Secretion for TH17 Differentiation.

Candida albicans is usually a benign member of the human gut microbiota, but can become pathogenic under certain circumstances, for example in an immunocompromised host. The innate immune system, in particular neutrophils and macrophages, constitutes a crucial first line of defense against fungal invasion, however adaptive immunity may provide long term protection and thus allow vaccination of at risk patients. While TH1 and TH17 cells are important for antifungal responses, the role of B cells and antibodies in protection from C. albicans infection is less well defined. In this study, we show that C. albicans hyphae but not yeast, as well as fungal cell wall components, directly activate B cells via MyD88 signaling triggered by Toll- like receptor 2, leading to increased IgG1 production. While Dectin-1 signals and specific recognition by the B cell receptor are dispensable for B cell activation in this system, TLR2/MyD88 signals cooperate with CD40 signals in promoting B cell activation. Importantly, recognition of C. albicans via MyD88 signaling is also essential for induction of IL-6 secretion by B cells, which promotes TH17 polarization in T-B cell coculture experiments. B cells may thus be activated directly by C. albicans in its invasive form, leading to production of antibodies and T cell help for fungal clearance.

Inflammasome-mediated GSDMD activation facilitates escape of Candida albicans from macrophages.

Candida albicans is the most common cause of fungal sepsis. Inhibition of inflammasome activity confers resistance to polymicrobial and LPS-induced sepsis; however, inflammasome signaling appears to protect against C. albicans infection, so inflammasome inhibitors are not clinically useful for candidiasis. Here we show disruption of GSDMD, a known inflammasome target and key pyroptotic cell death mediator, paradoxically alleviates candidiasis, improving outcomes and survival of Candida-infected mice. Mechanistically, C. albicans hijacked the canonical inflammasome-GSDMD axis-mediated pyroptosis to promote their escape from macrophages, deploying hyphae and candidalysin, a pore-forming toxin expressed by hyphae. GSDMD inhibition alleviated candidiasis by preventing C. albicans escape from macrophages while maintaining inflammasome-dependent but GSDMD-independent IL-1ß production for anti-fungal host defenses. This study demonstrates key functions for GSDMD in Candida's escape from host immunity in vitro and in vivo and suggests that GSDMD may be a potential therapeutic target in C. albicans-induced sepsis.