HUMAN CD4-CELLS PROLIFERATE TO HLA-DR+ ALLOGENEIC VASCULAR ENDOTHELIUM - IDENTIFICATION OF ACCESSORY INTERACTIONS( T)

Serially passaged human endothelial cell (EC) cultures will stimulate highly purified peripheral blood CD4+ T cells to proliferate if and on ly if the EC cultures are pretreated with IFN-gamma to induce de novo expression of MHC class II molecules, principally HLA-DR. HLA-DR-expre ssing EC alone appear sufficient to stimulate purified CD4+ T cell pro liferation without the involvement of other leukocyte populations, as indicated by the following observations: (1) we find no contaminating leukocytes in our EC cultures by FACS analysis or fluorescence microsc opy; specifically, there are no detectable CD45 or HLA-DR expressing c ells; (2) neither the EC cultures nor the purified CD4+ T cells contai n HLA-DR expressing cells detectable by polymerase chain reaction (PCR ) of reverse-transcribed mRNA; (3) the stimulatory capacity of the EC cultures is maintained through serial subculture and through low-densi ty replating, indicating that the stimulatory cell type must prolifera te in culture as well as EC; and (4) in contrast to MLRs, the response to EC cultures is not inhibited by pretreatment of the stimulator cel ls and/or responding T cells with the monocyte toxin L-leucine-O-methy l ester. We have used mAb to investigate the role of various EC and T cell surface molecules in the T cell response. mAb to HLA-DR and CD4 i nhibit proliferative responses of CD4+ T cells to EC cultures, as woul d be expected if T cells recognize and proliferate to IFN-gamma-induce d allogeneic class II MHC molecules; whereas, also as expected, mAb to class I MHC molecules were without effect. Proliferation is also inhi bited by mAbs to T cell CD2 and LFA-1 beta chain (CD18) and by mAbs to LFA-3 (CD58) and CD44, which are expressed by T cells and EC. mAb to ICAM-1 (CD54, a ligand for LFA-1) provides inconsistent inhibition, an d mAb to ICAM-2, used with or without anti-ICAM-1, is not inhibitory. Because both of these mAb block adhesion of LFA-1 expressing T cells t o EC, our data suggest that additional ligands for LFA-1 must be impor tant for allogeneic proliferation. mAb to VLA-4 alpha or beta chains ( CD49d, CD29) enhance proliferation, presumably through direct costimul ation of the T cells by these antibodies. However, a mAb to VCAM-1, an EC ligand for VLA-4, is partially inhibitory. In summary, our data su ggest that CD4+ T cells directly recognize allogeneic HLA-DR molecules on EC, and further interact with EC ligands via CD2, LFA-1, and CD44. EC LFA-3 appears to be an important costimulator of T cell responses, whereas interaction with EC ICAM-1, ICAM-2, and VCAM-1 appear to be l ess critical for induction of T cell responses.