Tfc cells promote B cell antibody class-switch in autoimmune disease. Allo-primed Tfc cells kill self IgG1+ B cells. Tfc cells express B cell costimulatory proteins, and promote B cell differentiation and Ab isotype class switching. CD8 T cells facilitate enhanced B cell expansion and Ab production in IL-2- KO mice. Here, IL2 is linked to autoimmune disease.