Analyses over several weeks after infection showed that unlike T. b. brucei AnTat 1.1-infected C57BL/6 mice, infected Prf1-/- mice retained B cell follicles, developed high-titer IgM and IgG, particularly IgG1, antibody responses against a wide range of trypanosome polypeptides, controlled trypanosome parasitemia, maintained their body weight and blood packed cell volume, and survived at least twice as long as similarly infected intact mice, which jointly are characteristics of trypanosomiasis resistance [7, 15, 29, 55, 56]. The gene discussed is PRF1; the disease is trypanosomiasis.