INDUCTION OF T-CELL ACTIVATION BY MONOCLONAL-ANTIBODIES SPECIFIC FOR THE TRANSFERRIN RECEPTOR

The effect of the monoclonal antibodies (mAb), FG 1/5, FG 1/6 and FG 2/12, specific for different epitopes of the transferrin receptor (TfR) on T cell activation was studied. mAb FG 1/6 but not FG 2/12 or FG 1/5 was able to induce T cell proliferation in presence of submitogenic doses of phorbol esters. The costimulatory effect of FG 1/6 was seen only with phorbol esters known to be activators of protein kinase C. This proliferation occurred at low concentration (0.5 μg/ml) of antibody, required the simultaneous presence of both stimuli, phorbol esters and FG 1/6, and was independent of the presence of accessory cells. Furthermore, FG 1/6 mAb was able to increase the rate of modulation of CD3 surface expression induced by phorbol esters. FG 1/6 induced interleukin (IL) 2 synthesis by normal and transformed T lymphocytes. In addition, anti‐IL 2 receptor antibodies inhibited FG 1/6 plus phorbol ester‐induced proliferation. Our results indicate that FG 1/6 mAb may provide to the T cells complementary signals to protein kinase C and that this activation is mediated by the IL 2/IL 2R pathway. Copyright © 1990 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim