Building on the hypothesis that CD8+ T-cell dependent cytolytic activity could play a major role in anti-sporozoite immunity, these original studies isolated MHC class II-restricted cytolytic CD4+ T cell clones that recognized a P. falciparum CSP derived epitope (human) and a P. berghei epitope common to both the liver and blood stage infection of this rodent parasite. The gene discussed is CD4; the disease is infection.