ROLE OF NITRIC-OXIDE AND MELANOGENESIS IN THE ACCOMPLISHMENT OF ANTICRYPTOCOCCAL ACTIVITY BY THE BV-2 MICROGLIAL CELL-LINE

In the present paper, we investigated the involvement of cryptococcal melanogenesis and macrophage nitric oxide (NO) production in the accom plishment of anticryptococcal activity by microglial effector cells, u sing the murine cell line BV-2. We demonstrate that the constitutive l evels of anticryptococcal activity exerted by BV-2 cells is significan tly enhanced upon interferon gamma plus lipopolysaccharide treatment. The phenomenon, which occurs with no enhancement of phagocytic activit y, is associated with the production of high levels of NO and is aboli shed by addition of N-G-monomethyl-L-arginine. Comparable patterns of results are observed employing either unopsonized or opsonized microbi al targets, the latter microorganisms being markedly more susceptible to BV-2 cell antimicrobial activity. Furthermore, melanization of Cryp tococcus neoformans significantly reduces its susceptibility to BV-2 a ntimicrobial activity, regardless of the fact that activated macrophag es or opsonized microorganisms have been employed. In conclusion, our results provide evidence that NO-dependent events are involved in the fulfillment of anticryptococcal activity by activated microglial cells and that fungal melanization is a precious escamotage through which C . neoformans overcomes host defenses.