Defense mechanisms of IFN-gamma and LPS-primed murine microglia against Acanthamoeba castellanii infection.

In the central nervous system (CNS), cytokine-primed microglia play a central role in host's defense against Acanthamoeba castellanii infection. In this study, the effect of recombinant interferon (rIFN)-gamma and Salmonella enterica serovar enteritidis lipopolysaccharide (LPS), both inflammatory stimuli, on A. castellanii infection in murine microglia was examined. Priming of microglia with rIFN-gamma and LPS synergistically triggered, in a dose-dependent manner, amebastatic activity in these cells. More than 52%, 88% or 95% of this function was then abrogated by anti-IL-1beta (but not anti-IL-1alpha), IL-6 or TNF-alpha neutralizing antibodies, suggesting that these endogenously produced cytokines may participate in the antimicrobial capacity. Consistent with these findings, the priming of microglia with rIFN-gamma and LPS elicited the release of proinflammatory interleukin (IL)-1alpha, IL-1beta, IL-6 and tumor necrosis factor (TNF)-alpha. Since L-canavanine affected amebastatic activity only during the priming process but not during the infection process, NO-dependent pathway appears to be not the sole antiparasitic mechanism involved in this function. These data suggest that rIFN-gamma and LPS, likely through a proinflammatory network, up-regulate the release of IL-beta, IL-6 and TNF-alpha, which could trigger antimicrobial activity against A. castellanii infection in the brain.