Glucose-enhanced oxidative stress resistance-A protective anticipatory response that enhances the fitness of Candida albicans during systemic infection.

Most microbes have developed responses that protect them against stresses relevant to their niches. Some that inhabit reasonably predictable environments have evolved anticipatory responses that protect against impending stresses that are likely to be encountered in their niches-termed "adaptive prediction". Unlike yeasts such as Saccharomyces cerevisiae, Kluyveromyces lactis and Yarrowia lipolytica and other pathogenic Candida species we examined, the major fungal pathogen of humans, Candida albicans, activates an oxidative stress response following exposure to physiological glucose levels before an oxidative stress is even encountered. Why? Using competition assays with isogenic barcoded strains, we show that "glucose-enhanced oxidative stress resistance" phenotype enhances the fitness of C. albicans during neutrophil attack and during systemic infection in mice. This anticipatory response is dependent on glucose signalling rather than glucose metabolism. Our analysis of C. albicans signalling mutants reveals that the phenotype is not dependent on the sugar receptor repressor pathway, but is modulated by the glucose repression pathway and down-regulated by the cyclic AMP-protein kinase A pathway. Changes in catalase or glutathione levels do not correlate with the phenotype, but resistance to hydrogen peroxide is dependent on glucose-enhanced trehalose accumulation. The data suggest that the evolution of this anticipatory response has involved the recruitment of conserved signalling pathways and downstream cellular responses, and that this phenotype protects C. albicans from innate immune killing, thereby promoting the fitness of C. albicans in host niches.

Immune cells fold and damage fungal hyphae.

Innate immunity provides essential protection against life-threatening fungal infections. However, the outcomes of individual skirmishes between immune cells and fungal pathogens are not a foregone conclusion because some pathogens have evolved mechanisms to evade phagocytic recognition, engulfment, and killing. For example, Candida albicans can escape phagocytosis by activating cellular morphogenesis to form lengthy hyphae that are challenging to engulf. Through live imaging of C. albicans-macrophage interactions, we discovered that macrophages can counteract this by folding fungal hyphae. The folding of fungal hyphae is promoted by Dectin-1, ß2-integrin, VASP, actin-myosin polymerization, and cell motility. Folding facilitates the complete engulfment of long hyphae in some cases and it inhibits hyphal growth, presumably tipping the balance toward successful fungal clearance.

Blocking two-component signalling enhances Candida albicans virulence and reveals adaptive mechanisms that counteract sustained SAPK activation.

The Ypd1 phosphorelay protein is a central constituent of fungal two-component signal transduction pathways. Inhibition of Ypd1 in Saccharomyces cerevisiae and Cryptococcus neoformans is lethal due to the sustained activation of the 'p38-related' Hog1 stress-activated protein kinase (SAPK). As two-component signalling proteins are not found in animals, Ypd1 is considered to be a prime antifungal target. However, a major fungal pathogen of humans, Candida albicans, can survive the concomitant sustained activation of Hog1 that occurs in cells lacking YPD1. Here we show that the sustained activation of Hog1 upon Ypd1 loss is mediated through the Ssk1 response regulator. Moreover, we present evidence that C. albicans survives SAPK activation in the short-term, following Ypd1 loss, by triggering the induction of protein tyrosine phosphatase-encoding genes which prevent the accumulation of lethal levels of phosphorylated Hog1. In addition, our studies reveal an unpredicted, reversible, mechanism that acts to substantially reduce the levels of phosphorylated Hog1 in ypd1Δ cells following long-term sustained SAPK activation. Indeed, over time, ypd1Δ cells become phenotypically indistinguishable from wild-type cells. Importantly, we also find that drug-induced down-regulation of YPD1 expression actually enhances the virulence of C. albicans in two distinct animal infection models. Investigating the underlying causes of this increased virulence, revealed that drug-mediated repression of YPD1 expression promotes hyphal growth both within murine kidneys, and following phagocytosis, thus increasing the efficacy by which C. albicans kills macrophages. Taken together, these findings challenge the targeting of Ypd1 proteins as a general antifungal strategy and reveal novel cellular adaptation mechanisms to sustained SAPK activation.

Calcineurin orchestrates dimorphic transitions, antifungal drug responses and host-pathogen interactions of the pathogenic mucoralean fungus Mucor circinelloides.

Calcineurin plays essential roles in virulence and growth of pathogenic fungi and is a target of the natural products FK506 and Cyclosporine A. In the pathogenic mucoralean fungus Mucor circinelloides, calcineurin mutation or inhibition confers a yeast-locked phenotype indicating that calcineurin governs the dimorphic transition. Genetic analysis in this study reveals that two calcineurin A catalytic subunits (out of three) are functionally diverged. Homology modeling illustrates modes of resistance resulting from amino substitutions in the interface between each calcineurin subunit and the inhibitory drugs. In addition, we show how the dimorphic transition orchestrated by calcineurin programs different outcomes during host-pathogen interactions. For example, when macrophages phagocytose Mucor yeast, subsequent phagosomal maturation occurs, indicating host cells respond appropriately to control the pathogen. On the other hand, upon phagocytosis of spores, macrophages fail to form mature phagosomes. Cytokine production from immune cells differs following exposure to yeast versus spores (which germinate into hyphae). Thus, the morphogenic transition can be targeted as an efficient treatment option against Mucor infection. In addition, genetic analysis (including gene disruption and mutational studies) further strengthens the understanding of calcineurin and provides a foundation to develop antifungal agents targeting calcineurin to deploy against Mucor and other pathogenic fungi.

Role of Dectin-2 for host defense against systemic infection with Candida glabrata.

Although Candida glabrata is an important pathogenic Candida species, relatively little is known about its innate immune recognition. Here, we explore the potential role of Dectin-2 for host defense against C. glabrata. Dectin-2-deficient (Dectin-2(-/-)) mice were found to be more susceptible to C. glabrata infections, showing a defective fungal clearance in kidneys but not in the liver. The increased susceptibility to infection was accompanied by lower production of T helper 1 (Th1) and Th17-derived cytokines by splenocytes of Dectin-2(-/-) mice, while macrophage-derived cytokines were less affected. These defects were associated with a moderate yet significant decrease in phagocytosis of the fungus by the Dectin-2(-/-) macrophages and neutrophils. Neutrophils of Dectin-2(-/-) mice also displayed lower production of reactive oxygen species (ROS) upon challenge with opsonized C. glabrata or C. albicans. This study suggests that Dectin-2 is important in host defense against C. glabrata and provides new insights into the host defense mechanisms against this important fungal pathogen.

The characterisation and determinants of quality of life in ANCA associated vasculitis.

OBJECTIVES: To contextualise and identify the determinants of poor health related quality of life (QOL) among patients with antineutrophil cytoplasm antibody (ANCA) associated vasculitis (AAV). METHODS: A multicentre AAV case-control study was conducted using two matched groups of population and chronic disease controls. Measures of physical and mental QOL as well as putative bio-psychosocial determinants of QOL impairment were collected. Concurrently, putative clinical QOL determinants were recorded. Conditional logistic regression analyses characterised group differences while multivariable logistic regression identified within-case QOL associations which were further quantified using population attributable risks (PAR). RESULTS: Cases (n=410) experienced similar QOL to chronic disease controls (n=318) (physical QOL: OR 0.7, 95% CI 0.4 to 1.1; mental QOL: OR 1.1, 95% CI 0.8 to 1.6). However, they were substantially more likely to report poor QOL compared to general population controls (n=470) (physical QOL: OR 7.0, 95% CI 4.4 to 11.1; mental QOL: OR 2.5, 95% CI 1.7 to 3.6). A few clinical, but many more bio-psychosocial factors were independently associated with poor QOL. In population terms, fatigue was found to be of principal importance (physical QOL: PAR 24.6%; mental QOL: PAR 47.4%). CONCLUSIONS: AAV patients experienced significant QOL impairment compared to the general population, but similar to those with other chronic diseases whose considerable needs are already recognised. Potentially modifiable clinical determinants have been identified; however bio-psychosocial interventions are likely to provide the greater QOL gains in this patient population.

Markers for work disability in anti-neutrophil cytoplasmic antibody-associated vasculitis.

OBJECTIVES: ANCA-associated vasculitis (AAV) commonly affects those of working age. Since survival rates have been transformed by immunotherapeutics, the measurement of other outcomes has become increasingly relevant. Work disability is an important outcome for both patient and society that has yet to be fully evaluated in AAV. We aimed to assess employment status in AAV patients and identify putative predictors of their work disability. METHODS: A cross-sectional study was undertaken. AAV cases were recruited according to consecutive clinic attendance. Subjects completed a questionnaire that determined employment status and other psychosocial measures. Clinical factors were concurrently recorded by the attending physician. From the data of those subjects of working age, a multivariable model was developed using forward stepwise logistic regression to identify the independent associations of work disability, defined by those subjects reporting unemployment secondary to ill-health. Results are expressed as odds ratios (ORs) and 95% CIs. RESULTS: Of the 410 participants (84.4% response rate), 149 (36.7%) were employed, 197 (48.6%) retired and 54 (13.3%) unemployed secondary to ill health. Of those of working age, 26.0% were considered work disabled. Fatigue (OR 7.1, 95% CI 1.5, 33.1), depression (OR 4.4, 95% CI 1.8, 10.8), severe disease damage [Vasculitis Damage Index (VDI) > 4 (OR 3.9, 95% CI 1.01, 14.7)] and being overweight (OR 3.4, 95% CI 1.3, 8.9) were independently associated with their unemployment. CONCLUSION: A quarter of working-age AAV subjects reported unemployment as a result of ill health and are characterized by high levels of fatigue, depression, disease damage and being overweight. These potentially modifiable factors may inform future multidisciplinary interventions aimed at alleviating work disability.

Sialoadhesin promotes rapid proinflammatory and type I IFN responses to a sialylated pathogen, Campylobacter jejuni.

Sialoadhesin (Sn) is a macrophage (Mφ)-restricted receptor that recognizes sialylated ligands on host cells and pathogens. Although Sn is thought to be important in cellular interactions of Mφs with cells of the immune system, the functional consequences of pathogen engagement by Sn are unclear. As a model system, we have investigated the role of Sn in Mφ interactions with heat-killed Campylobacter jejuni expressing a GD1a-like, sialylated glycan. Compared to Sn-expressing bone marrow-derived macrophages (BMDM) from wild-type mice, BMDM from mice either deficient in Sn or expressing a non-glycan-binding form of Sn showed greatly reduced phagocytosis of sialylated C. jejuni. This was accompanied by a strong reduction in MyD88-dependent secretion of TNF-α, IL-6, IL-12, and IL-10. In vivo studies demonstrated that functional Sn was required for rapid TNF-α and IFN-ß responses to i.v.-injected sialylated C. jejuni. Bacteria were captured within minutes after i.v. injection and were associated with Mφs in both liver and spleen. In the spleen, IFN-ß-reactive cells were localized to Sn⁺ Mφs and other cells in the red pulp and marginal zone. Together, these studies demonstrate that Sn plays a key role in capturing sialylated pathogens and promoting rapid proinflammatory cytokine and type I IFN responses.

Impact of secreted glucanases upon the cell surface and fitness of Candida albicans during colonisation and infection.

Host recognition of the pathogen-associated molecular pattern (PAMP), ß-1,3-glucan, plays a major role in antifungal immunity. ß-1,3-glucan is an essential component of the inner cell wall of the opportunistic pathogen Candida albicans. Most ß-1,3-glucan is shielded by the outer cell wall layer of mannan fibrils, but some can become exposed at the cell surface. In response to host signals such as lactate, C. albicans shaves the exposed ß-1,3-glucan from its cell surface, thereby reducing the ability of innate immune cells to recognise and kill the fungus. We have used sets of barcoded xog1 and eng1 mutants to compare the impacts of the secreted ß-glucanases Xog1 and Eng1 upon C. albicans in vitro and in vivo. Flow cytometry of Fc-dectin-1-stained strains revealed that Eng1 plays the greater role in lactate-induced ß-1,3-glucan masking. Transmission electron microscopy and stress assays showed that neither Eng1 nor Xog1 are essential for cell wall maintenance, but the inactivation of either enzyme compromised fungal adhesion to gut and vaginal epithelial cells. Competitive barcode sequencing suggested that neither Eng1 nor Xog1 strongly influence C. albicans fitness during systemic infection or vaginal colonisation in mice. However, the deletion of XOG1 enhanced C. albicans fitness during gut colonisation. We conclude that both Eng1 and Xog1 exert subtle effects on the C. albicans cell surface that influence fungal adhesion to host cells and that affect fungal colonisation in certain host niches.

A CO2 sensing module modulates ß-1,3-glucan exposure in Candida albicans.

Microbial species capable of co-existing with healthy individuals, such as the commensal fungus Candida albicans, exploit multifarious strategies to evade our immune defenses. These strategies include the masking of immunoinflammatory pathogen-associated molecular patterns (PAMPs) at their cell surface. We reported previously that C. albicans actively reduces the exposure of the proinflammatory PAMP, ß-1,3-glucan, at its cell surface in response to host-related signals such as lactate and hypoxia. Here, we show that clinical isolates of C. albicans display phenotypic variability with respect to their lactate- and hypoxia-induced ß-1,3-glucan masking. We have exploited this variability to identify responsive and non-responsive clinical isolates. We then performed RNA sequencing on these isolates to reveal genes whose expression patterns suggested potential association with lactate- or hypoxia-induced ß-1,3-glucan masking. The deletion of two such genes attenuated masking: PHO84 and NCE103. We examined NCE103-related signaling further because NCE103 has been shown previously to encode carbonic anhydrase, which promotes adenylyl cyclase-protein kinase A (PKA) signaling at low CO2 levels. We show that while CO2 does not trigger ß-1,3-glucan masking in C. albicans, the Sch9-Rca1-Nce103 signaling module strongly influences ß-1,3-glucan exposure in response to hypoxia and lactate. In addition to identifying a new regulatory module that controls PAMP exposure in C. albicans, our data imply that this module is important for PKA signaling in response to environmental inputs other than CO2.IMPORTANCEOur innate immune defenses have evolved to protect us against microbial infection in part via receptor-mediated detection of "pathogen-associated molecular patterns" (PAMPs) expressed by invading microbes, which then triggers their immune clearance. Despite this surveillance, many microbial species are able to colonize healthy, immune-competent individuals, without causing infection. To do so, these microbes must evade immunity. The commensal fungus Candida albicans exploits a variety of strategies to evade immunity, one of which involves reducing the exposure of a proinflammatory PAMP (ß-1,3-glucan) at its cell surface. Most of the ß-1,3-glucan is located in the inner layer of the C. albicans cell wall, hidden by an outer layer of mannan fibrils. Nevertheless, some ß-1,3-glucan can become exposed at the fungal cell surface. However, in response to certain specific host signals, such as lactate or hypoxia, C. albicans activates an anticipatory protective response that decreases ß-1,3-glucan exposure, thereby reducing the susceptibility of the fungus to impending innate immune attack. Here, we exploited the natural phenotypic variability of C. albicans clinical isolates to identify strains that do not display the response to ß-1,3-glucan masking signals observed for the reference isolate, SC5314. Then, using genome-wide transcriptional profiling, we compared these non-responsive isolates with responsive controls to identify genes potentially involved in ß-1,3-glucan masking. Mutational analysis of these genes revealed that a sensing module that was previously associated with CO2 sensing also modulates ß-1,3-glucan exposure in response to hypoxia and lactate in this major fungal pathogen of humans.

Explaining fatigue in ANCA-associated vasculitis.

OBJECTIVES: To identify the determinants of fatigue among patients with ANCA-associated vasculitis (AAV). METHODS: A multicentre cross-sectional study was conducted. Subjects fulfilling the European Medicines Agency criteria for granulomatosis with polyangiitis (Wegener's), microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis (Churg-Strauss) were approached according to consecutive clinic attendance and invited to complete a questionnaire assessing fatigue and putative biopsychosocial determinants of this symptom. Concurrently, potential clinical determinants were recorded. Independent associations of fatigue were identified using forward stepwise logistic regression modelling and their overall impact expressed as population attributable risk (PAR). RESULTS: The majority (74.8%) of participants (n = 410) reported high levels of fatigue that were found to be significantly associated with numerous biopsychosocial and clinical factors. Sleep disturbance [odds ratio (OR) 5.3, 95% CI 2.7, 10.5] and pain (OR 3.8, 95% CI 2.0, 7.3) were the strongest independent associations of fatigue and, on a population level, each was more than twice as important as any other putative determinant (PAR 18.1% and 16.5%, respectively). Female gender (OR 2.1, 95% 1.1, 4.0), elevated CRP (OR 3.7, 95% CI 1.7, 8.1) and the dysfunctional coping strategies of behavioural disengagement (OR 2.4, 95% CI 1.04, 5.6) and denial (OR 2.4, 95% CI 0.9, 6.7) were also independently associated with fatigue. CONCLUSION: The data suggest that AAV-related fatigue is multifactorial in origin. Sleep disturbance and pain were found to be most important, although inflammation, as measured by CRP, was also associated. This study has identified potentially modifiable determinants that will inform future interventions aimed at alleviating fatigue.

Fungal spore swelling and germination are restricted by the macrophage phagolysosome.

Many species of medically important fungi are prolific in the formation of asexual spores. Spores undergo a process of active swelling and cell wall remodelling before a germ tube is formed and filamentous growth ensues. Highly elongated germ tubes are known to be difficult to phagocytose and pose particular challenges for immune phagocytes. However, the significance of the earliest stages of spore germination during immune cell interactions has not been investigated and yet this is likely to be important for defence against sporogenous fungal pathogens. We show here that macrophages restrict the early phases of the spore germination process of Aspergillus fumigatus and Mucor circinelloides including the initial phase of spore swelling, spore germination and early polarised growth. Macrophages are therefore adept at retarding germination as well as subsequent vegetative growth which is likely to be critical for immune surveillance and protection against sporulating fungi.

Erratum to "The nature of the fungal cargo induces significantly different temporal programmes of macrophage phagocytosis" [Cell Surf. 8 (2022) 100082].

[This corrects the article DOI: 10.1016/j.tcsw.2022.100082.].

The nature of the fungal cargo induces significantly different temporal programmes of macrophage phagocytosis.

Phagocytosis is an essential component of our immune defence against fungal pathogens. Differences in the dynamics of phagocyte migration, recognition, uptake and phagolysosome maturation are dependent on the characteristics of the fungal cargo, and in particular to differences in cell wall composition and cellular morphology. However, studies that have focused on phagocyte interactions with individual fungal species have not enabled comparisons in the kinetics of these interactions to be made between these different species. We therefore used live cell video microscopy to examine the temporal dynamics of phagocytosis for a range of fungal cargoes by thioglycollate-elicited peritoneal macrophages from C57BL/6 mice. Uniform populations of macrophages were challenged at the same time with yeast cells of Candida albicans, Candida glabrata, Saccharomyces cerevisiae and Cryptococcus neoformans (wild-type and an acapsular mutant, cap59Δ), and spores of Aspergillus fumigatus and Mucor circinelloides to enable standardized comparative interactions to be quantified from different stages of phagocytosis. Differences in the rate of uptake of fungal cells varied by up to 26-fold, whilst differences in time to induce phagosome acidification varied by as much as 29-fold. Heat-killing or opsonizing the fungal targets markedly affected the kinetics of the interaction in a species-specific manner. Fungal and macrophage killing assays further revealed cargo-specific differences in phagocytosis and diversity in fungal evasion mechanisms. Therefore, simultaneous assessment of the interaction of macrophages with different fungal pathogens highlighted major differences in the kinetics and growth responses during fungus-phagocyte interactions that are likely to impact on pathogenesis and virulence.

Impact of changes at the Candida albicans cell surface upon immunogenicity and colonisation in the gastrointestinal tract.

The immunogenicity of Candida albicans cells is influenced by changes in the exposure of microbe-associated molecular patterns (MAMPs) on the fungal cell surface. Previously, the degree of exposure on the C. albicans cell surface of the immunoinflammatory MAMP ß-(1,3)-glucan was shown to correlate inversely with colonisation levels in the gastrointestinal (GI) tract. This is important because life-threatening systemic candidiasis in critically ill patients often arises from translocation of C. albicans strains present in the patient's GI tract. Therefore, using a murine model, we have examined the impact of gut-related factors upon ß-glucan exposure and colonisation levels in the GI tract. The degree of ß-glucan exposure was examined by imaging flow cytometry of C. albicans cells taken directly from GI compartments, and compared with colonisation levels. Fungal ß-glucan exposure was lower in the cecum than the small intestine, and fungal burdens were correspondingly higher in the cecum. This inverse correlation did not hold for the large intestine. The gut fermentation acid, lactate, triggers ß-glucan masking in vitro, leading to attenuated anti-Candida immune responses. Additional fermentation acids are present in the GI tract, including acetate, propionate, and butyrate. We show that these acids also influence ß-glucan exposure on C. albicans cells in vitro and, like lactate, they influence ß-glucan exposure via Gpr1/Gpa2-mediated signalling. Significantly, C. albicans gpr1Δ gpa2Δ cells displayed elevated ß-glucan exposure in the large intestine and a corresponding decrease in fungal burden, consistent with the idea that Gpr1/Gpa2-mediated ß-glucan masking influences colonisation of this GI compartment. Finally, extracts from the murine gut and culture supernatants from the mannan grazing gut anaerobe Bacteroides thetaiotaomicron promote ß-glucan exposure at the C. albicans cell surface. Therefore, the local microbiota influences ß-glucan exposure levels directly (via mannan grazing) and indirectly (via fermentation acids), whilst ß-glucan masking appears to promote C. albicans colonisation of the murine large intestine.

Nature of ß-1,3-Glucan-Exposing Features on Candida albicans Cell Wall and Their Modulation.

Candida albicans exists as a commensal of mucosal surfaces and the gastrointestinal tract without causing pathology. However, this fungus is also a common cause of mucosal and systemic infections when antifungal immune defenses become compromised. The activation of antifungal host defenses depends on the recognition of fungal pathogen-associated molecular patterns (PAMPs), such as ß-1,3-glucan. In C. albicans, most ß-1,3-glucan is present in the inner cell wall, concealed by the outer mannan layer, but some ß-1,3-glucan becomes exposed at the cell surface. In response to host signals, such as lactate, C. albicans induces the Xog1 exoglucanase, which shaves exposed ß-1,3-glucan from the cell surface, thereby reducing phagocytic recognition. We show here that ß-1,3-glucan is exposed at bud scars and punctate foci on the lateral wall of yeast cells, that this exposed ß-1,3-glucan is targeted during phagocytic attack, and that lactate-induced masking reduces ß-1,3-glucan exposure at bud scars and at punctate foci. ß-1,3-Glucan masking depends upon protein kinase A (PKA) signaling. We reveal that inactivating PKA, or its conserved downstream effectors, Sin3 and Mig1/Mig2, affects the amounts of the Xog1 and Eng1 glucanases in the C. albicans secretome and modulates ß-1,3-glucan exposure. Furthermore, perturbing PKA, Sin3, or Mig1/Mig2 attenuates the virulence of lactate-exposed C. albicans cells in Galleria. Taken together, the data are consistent with the idea that ß-1,3-glucan masking contributes to Candida pathogenicity. IMPORTANCE Microbes that coexist with humans have evolved ways of avoiding or evading our immunological defenses. These include the masking by these microbes of their "pathogen-associated molecular patterns" (PAMPs), which are recognized as "foreign" and used to activate protective immunity. The commensal fungus Candida albicans masks the proinflammatory PAMP ß-1,3-glucan, which is an essential component of its cell wall. Most of this ß-1,3-glucan is hidden beneath an outer layer of the cell wall on these microbes, but some can become exposed at the fungal cell surface. Using high-resolution confocal microscopy, we examine the nature of the exposed ß-1,3-glucan at C. albicans bud scars and at punctate foci on the lateral cell wall, and we show that these features are targeted by innate immune cells. We also reveal that downstream effectors of protein kinase A (Mig1/Mig2, Sin3) regulate the secretion of major glucanases, modulate the levels of ß-1,3-glucan exposure, and influence the virulence of C. albicans in an invertebrate model of systemic infection. Our data support the view that ß-1,3-glucan masking contributes to immune evasion and the virulence of a major fungal pathogen of humans.

Glycosylation status of the C. albicans cell wall affects the efficiency of neutrophil phagocytosis and killing but not cytokine signaling.

The cell wall of the opportunistic human fungal pathogen, Candida albicans is a complex, layered network of rigid structural polysaccharides composed of ß-glucans and chitin that is covered with a fibrillar matrix of highly glycosylated mannoproteins. Polymorphonuclear cells (PMNs, neutrophils) are the most prevalent circulating phagocytic leukocyte in peripheral blood and they are pivotal in the clearance of invading fungal cells from tissues. The importance of cell-wall mannans for the recognition and uptake of C. albicans by human PMNs was therefore investigated. N- and O-glycosylation-deficient mutants were attenuated in binding and phagocytosis by PMNs and this was associated with reduced killing of C. albicans yeast cells. No differences were found in the production of the respiratory burst enzyme myeloperoxidase (MPO) and the neutrophil chemokine IL-8 in PMNs exposed to control and glycosylation-deficient C. albicans strains. Thus, the significant decrease in killing of glycan-deficient C. albicans strains by PMNs is a consequence of a marked reduction in phagocytosis rather than changes in the release of inflammatory mediators by PMNs.

A novel 4-dimensional live-cell imaging system to study leukocyte-endothelial dynamics in ANCA-associated vasculitis.

Neutrophils, monocytes and the endothelium are critical to ANCA-associated vasculitis (AAV) pathogenesis. This study aimed to develop a 4-dimensional (4D) live-cell imaging system that would enable investigation of spatial and temporal dynamics of these cells in health and disease. We further aimed to validate this system using autologous donor serum from AAV patients and polyclonal ANCA IgG, as well as exploring its potential in the pre-clinical testing of putative therapeutic compounds. Neutrophils and monocytes were isolated from peripheral venous blood of AAV patients or healthy controls and co-incubated on an endothelial monolayer in the presence of autologous serum. Alternatively, polyclonal ANCA IgG was used, following TNF-α priming, and imaged in 4-dimensions for 3 h using a spinning disc confocal microscope. Volocity 6.3® analysis software was used for quantification of leukocyte dynamics. The use of autologous serum resulted in increased neutrophil degranulation (p = .002), transmigration (p = .0096) and monocyte transcellular transmigration (p = .0013) in AAV patients. Polyclonal MPO-ANCA IgG induced neutrophil degranulation (p < .001) in this system. C5aR1 antagonism reduced neutrophil degranulation (p < .0002). We have developed a novel 4D in vitro system that allows accurate quantification of multiple neutrophil- and monocyte-endothelial interactions in AAV in a single assay. This system has the potential to highlight dynamics key to pathophysiology of disease, as well investigating the impact of potential therapeutics on these functions.

Epitope Shaving Promotes Fungal Immune Evasion.

The cell wall provides a major physical interface between fungal pathogens and their mammalian host. This extracellular armor is critical for fungal cell homeostasis and survival. Fungus-specific cell wall moieties, such as ß-1,3-glucan, are recognized as pathogen-associated molecular patterns (PAMPs) that activate immune-mediated clearance mechanisms. We have reported that the opportunistic human fungal pathogen Candida albicans masks ß-1,3-glucan following exposure to lactate, hypoxia, or iron depletion. However, the precise mechanism(s) by which C. albicans masks ß-1,3-glucan has remained obscure. Here, we identify a secreted exoglucanase, Xog1, that is induced in response to lactate or hypoxia. Xog1 functions downstream of the lactate-induced ß-glucan "masking" pathway to promote ß-1,3-glucan "shaving." Inactivation of XOG1 blocks most but not all ß-1,3-glucan masking in response to lactate, suggesting that other activities contribute to this phenomenon. Nevertheless, XOG1 deletion attenuates the lactate-induced reductions in phagocytosis and cytokine stimulation normally observed for wild-type cells. We also demonstrate that the pharmacological inhibition of exoglucanases undermines ß-glucan shaving, enhances the immune visibility of the fungus, and attenuates its virulence. Our study establishes a new mechanism underlying environmentally induced PAMP remodeling that can be manipulated pharmacologically to influence immune recognition and infection outcomes.IMPORTANCE The immune system plays a critical role in protecting us against potentially fatal fungal infections. However, some fungal pathogens have evolved evasion strategies that reduce the efficacy of our immune defenses. Previously, we reported that the fungal pathogen Candida albicans exploits specific host-derived signals (such as lactate and hypoxia) to trigger an immune evasion strategy that involves reducing the exposure of ß-glucan at its cell surface. Here, we show that this phenomenon is mediated by the induction of a major secreted exoglucanase (Xog1) by the fungus in response to these host signals. Inactivating XOG1-mediated "shaving" of cell surface-exposed ß-glucan enhances immune responses against the fungus. Furthermore, inhibiting exoglucanase activity pharmacologically attenuates C. albicans virulence. In addition to revealing the mechanism underlying a key immune evasion strategy in a major fungal pathogen of humans, our work highlights the potential therapeutic value of drugs that block fungal immune evasion.

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.