The effects of interleukin-15 on human gamma delta T cell responses to Plasmodium falciparum in vitro

We observed that the gamma delta T cell subset expands when human peripheral blood mononuclear cells (PBMC) from malaria-naive donors are cultured with Plasmodium falciparum lysate in the presence of IL-2 or IL-15, cytokines that utilize two common IL-2 receptor subunits. IL-15 induced the expansion of the gamma delta T cell subset at all levels tested, whereas IL-2 was not stimulatory at high levels. Flow cytometric analysis of apoptosis using the TUNEL assay indicated that the percentage and absolute number of gamma delta T cells undergoing apoptosis were greater in cultures stimulated with antigen and IL-2 than in cultures stimulated with either antigen and IL-15 or control erythrocyte lysate and IL-2. The ability of IL-15 to enhance gamma delta T cell function was also assessed; the results suggest that IL-15 can function with IL-2 to enhance the capacity of gamma delta T cells to inhibit parasite replication. Together these data indicate that IL-2 and IL-15, which both bind to IL-2R beta and IL-2R gamma c, enhance gamma delta T cell function, but they appear to have different effects on proliferation and survival.