Transitions between yeast and hyphae are essential for C. albicans pathogenesis. We found that Hbr1 is a positive and negative regulator of hyphal invasion (190). During embedded growth at 24 degrees C, a HBR1/hbr1 strain formed constitutively filamentous colonies throughout the matrix, resembling a mutant lacking EFG1, a major cAMP-dependent transcription factor that limits hyphal differentiation (193,194). Farnesol, a quorum sensing molecule that inhibits filamentation of WT C. albicans in a cAMP-dependent manner (195,196), perturbed the filamentation of HBR1/hbr1 cells, producing pseudohyphae-like cells lacking septa, whereas farnesol treated EFG1-null cells produced abundant opaque-like cells. Point mutations in the Hbr1 ATP-binding site caused distinct filamentation phenotypes including uniform radial hyphae, hyphal sprouts, and massive yeast cell production. Conversely, aerobic surface colonies of the HBR1 heterozygote on Spider and GlcNAc media lacked filamentation, which could be rescued by growth under 5% O2. Consistent with these morphogenesis defects, the HBR1 heterozygote exhibited attenuated virulence in a mouse candidemia model. These data define Hbr1 as an ATP-dependent positive and negative regulator of hyphal development that is sensitive to hypoxia. CD47 is a widely expressed receptor that regulates immunity by engaging its counter-receptor SIRP-alpha on phagocytes and its secreted ligand thrombospondin-1. Mice lacking CD47 can exhibit enhanced or impaired host responses to bacterial pathogens, but its role in fungal immunity has not been examined. cd47-/- mice on a C57BL/6 background showed significantly increased morbidity and mortality following Candida albicans infection when compared with wild-type mice. Despite normal fungal colonization at earlier times, cd47-/- mice at four days post-infection had increased colonization of brain and kidneys accompanied by stronger inflammatory reactions. Neutrophil and macrophage numbers were significantly elevated in kidneys and neutrophils in the brains of infected cd47-/- mice. However, no defect in phagocytic activity towards C. albicans was observed in cd47-/- bone-marrow-derived macrophages, and neutrophil and macrophage killing of C. albicans was not impaired. CD47-deficiency did not alter the early humoral immune response to C. albicans. Th1, Th2, and Th17 population of CD4+ T cells were expanded in the spleen, and gene expression profiles of spleen and kidney showed stronger pro-inflammatory signaling in infected cd47-/- mice. The chemoattractant chemokines MIP-2alpha and MIP-2beta were highly expressed in infected spleens of cd47-/- mice. G-CSF, GM-CSF, and the inflammasome component NLRP3 were more highly expressed in infected cd47-/- kidneys than in infected wild-type controls. Circulating pro- (TNF-alpha, IL-6) and anti-inflammatory cytokines (IL-10) were significantly elevated, but IL-17 was decreased. These data indicate that CD47 plays protective roles against disseminated candidiasis and alters pro-inflammatory and immunosuppressive pathways known to regulate innate and T cell immunity.
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