CFSE-labeled CD8 OT-I T cells alone or together with naïve CD4 T cells or CD4 Treg isolated from the livers of TF-OVA mice suffering from hepatitis were stimulated by incubation with spleen cells from TF-OVA mice, which have accumulated the endogenous antigen in vivo and are capable of stimulating OT-I T cells [13]. The gene discussed is CD4; the disease is hepatitis A virus infection.