Both CD4+ and CD8+ human lymphocytes are activated and proliferate in response to Cryptococcus neoformans

The current studies were performed to determine the contribution of T-cell subsets to lymphocyte proliferation in response to Cryptococcus neoformans, the most common invasive mycosis in acquired immune deficiency syndrome. We demonstrate for the first time that both human CD4 and CD8 cells are activated in response to C. neoformans. Both CD4 and CD8 cells express interleukin-2 receptor alpha (IL-2R alpha) and transferrin receptor and proliferate in response to C, neoformans, however proliferation of CD8 cells was dependent upon CD4 cells. The requirement for CD4 cells was complex, since CD8 enriched cells failed to express mRNA for IL-2, suggesting that CD4-dependent IL-2 production was required for CD8-cell proliferation. However, IL-2 was not sufficient to restore CD8-cell proliferation. These studies provide experimental evidence in humans to support the clinical impression that CD4 cells are important in cryptococcosis, and suggest that the appropriate CD4-derived signals could allow CD8 cells to assist in host defence.