Moreover, a virus vaccine expressing a parasite Ag prevented the development of proapoptotic CD8 T cells and promoted immunity, comprising both cytotoxic and cytokine-expressing CD8 T cells.27 Based on these and previous findings, we consider two major, but not exclusive, hypotheses to explain modulation of parasite infection by treatment with anti-FasL. The gene discussed is FASLG; the disease is parasitic infectious disease.