Protective tolerance to fungi: the role of IL-10 and tryptophan catabolism.

The pro-inflammatory-anti-inflammatory signaling balance is required for successful host-fungus interactions. The occurrence and interference of regulatory T (T-reg) cells in fungal infections offers a valuable framework for events that occur at the host-fungus interface. Control of both the class and magnitude of the immune response might confer an evolutionary advantage whereby the host effectively fights infection but limits collateral immunopathology. Alternatively, fungus-induced immunosuppression could be a powerful immunoevasion strategy for the invading pathogen. Discovery of T-reg cells as a source of IL-10 might contribute to a better understanding of the opposing functions and variable levels of production of this prototypic immunoregulatory cytokine in fungal infections and inflammatory diseases. T-reg cells, however, might also represent an additional mechanistic level at which host responses are subverted by fungi.