Natural killer cell-mediated cytotoxicity in cryptococcal meningitis.

There are evidences regarding the role of NK cytotoxic activity in the resistance against experimental C. neoformans infection. To assess the status of NK cell activity in human C. neoformans infection, we studied the peripheral blood of twelve patients with cryptococcal meningitis, six patients with CNS disease different to cryptococcal meningitis, and twelve healthy subjects. The number of CD16+cells and the NK cytotoxic activity of peripheral blood mononuclear cells was studied. The in vitro effect of exogenous IL-2 and interferon gamma on such cytotoxic activity was also studied. The number of CD16+ cells was not significantly different in patients compared to controls. However, cryptococcal patients exhibited a significant lower NK activity compared to both control groups (p less than 0.05 in both cases). The low NK activity of cryptococcal patients was fully reconstituted in vitro with the addition of rIL-2 but not with rIFN gamma. In vitro experiments suggest that the low NK activity of cryptococcal meningitis patients is not due to amphotericin B therapy or blockade of NK cells by C. neoformans-derived molecules. The results of this study suggests that patients with cryptococcal meningitis have a defective NK cytotoxic function and may aid to understand the pathogenesis of this disease.