LIGATION OF MHC CLASS-I MOLECULES ON PERIPHERAL-BLOOD T-LYMPHOCYTES INDUCES NEW PHENOTYPES AND FUNCTIONS

Microgram concentrations of immobilized anti-MHC class I (MHC-I) Ab in duced proliferation of resting CD3(+) T cells from peripheral blood, I n contrast, soluble Ab did not activate T cells, Exposure of T cells t o immobilized anti-MHC-I Ab for only 24 h was followed by proliferatio n and development or T cell-mediated cytotoxicity. Immediately followi ng MHC-I ligation, the T cells responded with increased protein tyrosi ne phosphorylation, with new bands appearing in the SDS-PAGE, Exposure of T cells to immobilized anti-MHC-I Ab for 24 h induced an increased surface expression of the TCR/CD3 and CD28 molecules, MHC-I-induced p roliferation of purified T cells was dependent on cellular interaction s with non-T cells. Under certain conditions, in which MHC-I was ligat ed by picogram concentrations of immobilized anti-MHC-I Ab, anti-TCR/C D3 Ah-induced proliferation of T cells was stongly inhibited, These da ta clearly demonstrate that ligation of the MHC-I complex on T cells m ay induce both positive and negative signals, Since the physiologic li gands for MHC-I molecules are TCR and the CD8 molecules, our data may suggest that IMHC-I molecules are instrumental in cellular interaction s between T cells.