Functional activities of antibodies against brain-associated T cell antigens. I. Induction of T cell proliferation.

Rabbit anti-mouse brain antiserum mediated an in vitro cooperative interaction between Ig-anti-Ig column-purified Lyt-1+, Lyt-2- T cells and spleen B cells. DNA synthesis in the B cells was inhibited with mitomycin C, and the T cell proliferative response was measured by [3H]thymidine incorporation after 24 h of culture. The T-B cell interaction was genetically unrestricted, and the accessory function of the B cell was engaged via interaction with the Fc portion of the T cell-bound anti-mouse brain antibody since the F(ab')2 fragment was inactive. The rabbit anti-mouse brain anti-serum appears to recognize a unique antigenic determinant in the T cell membrane which triggers proliferation. Although brain-absorbed, rabbit anti-mouse thymocyte antiserum contained antibodies which bound to the T cell surface, it was incapable of inducing T cell proliferation. Furthermore, the Thy-1 molecule itself did not appear to be involved because allo- and xenoantisera against the allelic determinants were inactive, and the capping of Thy-1.2 from the T cell surface did not prevent the binding of the mitogenic component in rabbit anti-mouse brain antiserum. The T cell reaction to anti-brain antiserum is unlike the antigen-specific T cell response in being genetically unrestricted. It is possible that the antibody operates via the perturbation of a T cell determinant involved in the binding of T cell growth factors, and/or reception of B cell feedback signals.