Biomolecular events involved in anticryptococcal resistance in the brain

We have recently shown that intracerebral (i.c.) administration of heat-killed Cryptococcus neoformans (HCN) enhances mouse resistance to a subsequent local challenge with lethal doses of viable yeast cells. Here we show that i.c. administration of HCN is also effective in significantly delaying brain colonization of mice intravenously infected with viable C. neoformans. PCR analysis revealed that interleukin 6 (IL-6) and IL-1 beta gene expression occurs in brain of HCN-treated mice but not in brains of saline-treated controls. In contrast, no differences are observed in terms of tumor necrosis factor alpha and IL-1 alpha gene transcripts, which are slightly and highly detectable, respectively, in saline-treated mice and which remain such also following HCN treatment. Furthermore, i.c. administration of exogenous IL-6 or IL-1 beta, but not tumor necrosis factor alpha, before local challenge with viable C. neoformans results in significantly reduced microbial counts in the brain and blood and in increased mouse survival. Taken together, these observations provide initial evidence that brain anticryptococcal resistance involves elicitation of a local cytokine response, involving primarily IL-6 and IL-1 beta.