In the mouse model of lymphocytic choriomeningitis virus (LCMV)-induced hepatitis, CD8+ T cell function was dependent on CD4+ T helper cell responses.19 That was shown by the observation that CD8+ T cell function was reduced in the absence of CD4+ T cells.19 Moreover, as shown in the non-human primate model of HCV infection, protective CD8+ T cell immunity may require CD4+ T helper cells not only in the primary infection but also after recovery, at the time of re-challenge.20 The gene discussed is CD8A; the disease is infection.