Differential IL-17 production and mannan recognition contribute to fungal pathogenicity and commensalism.

In this study, we present evidence of differential Th17 responses in human monocyte-derived dendritic cells exposed to the pathogenic Candida albicans or the nonpathogenic Saccharomyces cerevisiae. We use different forms of the microorganisms, cells, hyphae, and spores, as a toolbox to dissect the role of surface mannan in the fungal immune response. In contrast to the S. cerevisiae yeast cell-induced Th1 response, dendritic cells stimulated with spores or C. albicans hyphae induce cellular responses shifted toward Th17 differentiation. The differential recognition of specific mannan structures is the master regulator of the discrimination between harmful and harmless fungi. The switch between spores and yeast is crucial for the commensalism of S. cerevisiae and depends on the use of a different receptor repertoire. Understanding the role of cell wall recognition during infection might lead to understanding the boundaries between safety and pathogenicity.