MyD88 is dispensable for resistance to Paracoccidioides brasiliensis in a murine model of blood-borne disseminated infection.

We have studied the role of MyD88, an adaptor protein of Toll-like receptors (TLRs), in murine defenses against Paracoccidioides brasiliensis in a model of blood-borne disseminated infection. Wild-type (WT) and MyD88-deficient mice infected intravenously with P. brasiliensis yeast cells showed an equivalent fungal burden, as well as similar levels of proinflammatory IL-1beta, IL-6, IL-12p70, tumor necrosis factor (TNF)-alpha and MIP-2, T-helper type 1 (Th1) (IFN-gamma) and Th2 cytokines (IL-4) in tissue homogenates. In vitro production of TNF-alpha, IFN-gamma and IL-12p70, by antigen-stimulated splenocytes from infected animals, was also similar in both types of mice; this production of Th1 cytokines correlated with a similar frequency of IFN-gamma-producing CD4 T cells. Recruitment of neutrophils to the peritoneal cavity of intraperitoneally infected mice was not affected in TLR2-/-, TLR4-/- as compared with WT mice, but significantly decreased in MyD88-deficient mice. In vitro production of TNF-alpha by peritoneal macrophages from MyD88-, TLR2- and TLR4-deficient mice in response to P. brasiliensis yeasts was undiminished, as compared with macrophages from WT mice, and, in addition, laminarin failed to inhibit production of TNF-alpha by WT and MyD88-deficient macrophages. Overall, these data suggest that the response to P. brasiliensis yeasts occurs independently of the adaptor molecule MyD88, and indicate that TLR2, TLR4 and dectin-1 do not play a significant role in recognition of P. brasiliensis yeast cells.