Switch of CD8 T Cells to Noncytolytic CD8 ⁻ CD4 ⁻ Cells that Make T H 2 Cytokines and Help B Cells

CD8 + T cells are a major defense against viral infections and intracellular parasites. Their production of interferon-γ (IFN-γ) and their cytolytic activity are key elements in the immune response to these pathogens. Mature mouse CD8 + T cells that were activated in the presence of interleukin-4 (IL-4) developed into a CD8 - CD4 - population that was not cytolytic and did not produce IFN-γ. However, these CD8 - cells produced large amounts of IL-4, IL-5, and IL-10 and helped activate resting B cells. Thus, CD8 effector functions are potentially diverse and could be exploited by infectious agents that switch off host protective cytolytic responses.