BOTH CD4(-LYMPHOCYTES ARE ACTIVATED AND PROLIFERATE IN RESPONSE TO CRYPTOCOCCUS-NEOFORMANS() AND CD8(+) HUMAN)

The current studies were performed to determine the contribution of T- cell subsets to lymphocyte proliferation in response to Cryptococcus n eoformans, the most common invasive mycosis in acquired immune deficie ncy syndrome. We demonstrate for the first time that both human CD4 an d CD8 cells are activated in response to C. neoformans. Both CD4 and C D8 cells express interleukin-2 receptor alpha (IL-2R alpha) and transf errin receptor and proliferate in response to C. neoformans, however p roliferation of CD8 cells was dependent upon CD4 cells. The requiremen t for CD4 cells was complex, since CD8-enriched cells failed to expres s mRNA for IL-2 suggesting that CD4-dependent IL-2 production was requ ired for CD8-cell proliferation. However, IL-2 was not sufficient to r estore CD8-cell proliferation. These studies provide experimental evid ence in humans to support the clinical impression that CD4 cells are i mportant in cryptococcosis, and suggest that the appropriate CD4-deriv ed signals could allow CD8 cells to assist in host defence.