Biologic functions of the OKT1 T cell surface antigen. I. The T1 molecule is involved in helper function.

The OKT1 (Leu-1) monoclonal antibody reacts with a 69 KD glycoprotein that is present on only a fraction of functionally mature thymocytes but is maintained on most peripheral T cells. In the study presented, we examined the role of this surface molecule in T cell function. We found that addition of the OKT1 antibody to B cells and autologous T4+ cells markedly enhances B cell differentiation. This enhancement was apparent when nonirradiated or irradiated T4+ cells but not T8+ cells were used. Moreover, the OKT1 antibody as well as the OKT1 F(ab')2 fragment enhanced B cell differentiation in a dose-dependent fashion. It is important to note that perturbation of the T1 molecule with OKT1 in the presence of autologous E- cells causes the rapid release of molecules that trigger B cells to proliferate and differentiate into Ig-secreting cells. These data when considered together suggest that OKT1 reacts with a T cell membrane determinant or a complex that is intimately involved in the execution of helper function on OKT4+ cells.