T cell recognition of the Sm nuclear antigen: induction of T cell proliferative responses in MRL/Mp- +/+ mice.

The role of T cell immunity against nuclear antigens recognized by autoantibodies in human and murine systemic lupus is unclear. We have studied the T cell proliferative response to purified Sm nuclear antigen by measuring in vitro 3H-thymidine incorporation by MRL/Mp- +/+ lymph node cells primed with Sm in Freund's adjuvant. Sm-primed cells responded in a dose-dependent fashion when cultured in vitro with purified Sm. Absorption of the Sm with solid-phase anti-Sm IgG from either of two lupus patients ablated the response, whereas control absorptions with normal IgG had no effect. Furthermore, cells from mice primed with physicochemically purified Sm responded in vitro to affinity-purified antigen, and vice versa. Treatment of cells with either anti-Thy-1 or anti-Lyt-1 and C eliminated Sm-induced proliferation, whereas anti-Lyt-2 treatment resulted in enhanced responses. MRL/Mp- +/+ mice, which made no detectable anti-Sm antibodies in vivo, were nonetheless capable of generating Sm-reactive T cells. These results indicate that T cells can specifically recognize the Sm nuclear antigen. Such recognition may be of importance in the generation of antibodies to Sm and other nuclear antigens in vivo.