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Appearance of a proliferation-associated antigen, gp125, on rat and human lymphocytes by co-stimulation with phorbol ester and calcium ionophore.

A murine monoclonal antibody, B3, to rat cells and monoclonal antibody HBJ127 to human cells were found previously to recognize the homologous cell surface antigen systems (gp125) which are predominantly expressed on proliferating cells in the respective species. Biochemical signals required for the induction of gp125 antigen, and the kinetics of the antigen appearance were examined by use of lymphocytes. Costimulation with a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), and a calcium ionophore, A23187, resulted in strong induction of the gp125 antigen and subsequent DNA synthesis. The effect of TPA plus A23187 on rat T cells was diminished by EGTA, but recovered when CaCl2 was added. Human lymphocytes were also stimulated with TPA plus A23187 for the human gp125 induction. Dibutyryl cAMP and forskolin showed inhibitory effect on both gp125 antigen appearance and DNA synthesis in TPA/A23187-stimulated rat T cells whereas dibutyryl cGMP did not affect the gp125 antigen induction. Kinetic studies revealed that the appearance of the gp125 antigen on TPA/A23187-stimulated lymphocytes was faster than that of transferrin receptor in both rat and human systems. These results suggest regulatory roles of protein kinase C and Ca2+ in the induction of the gp125 antigen in the early phase of lymphocyte activation.