Accelerated expression of anti-Sm and Y2 idiotype differ in dependence on T cell subsets in MRL/+ mice

We investigated the role of MRL T cells in the induction of anti-Sm antibodies and Y2 idiotype. Four injections of Sm antigen in Freund's complete adjuvant were required to induce peak amounts of specific anti-Sm antibody in young BALB/c and MRL/+ mice. The Y2 idiotype was expressed in MRL/+ mice but not in BALB/c mice. Expression of both anti-Sm, predominantly IgG2a heavy chain, and Y2 idiotype was augmented in MRL/+ mice after two injections of Sm if, prior to immunization, mice received splenic T cells from naive MRL/lpr or immunized, but not naive MRL/+ mice. These results suggest that the lpr gene contributes to the ability of autoimmune T cells to augment the anti-Sm antibody response. Treatment of primed MRL/+ donor T cells with anti-CD4, but not anti-CD8, antibodies and complement removed the ability to augment anti-Sm antibody production. In contrast, augmentation of Y2 idiotype production was abrogated by pretreatment of donor T cells with either anti-CD4 or anti-CD8. These results suggest that, while MRL/+ CD4+ T cells play an important role in anti-Sm antibody production, additional interaction between CD4+ and CD8⁺ T cells augments Y2 expression.