Inhibition of proliferative and cytotoxic activities of human T lymphocytes with rabbit antibodies directed against leucoagglutinin‐reactive T cell surface components

Three rabbit antisera (870, 872 and 873) were raised against leucoagglutinin-reactive components from the surface of human T cells. The antibodies reacted with two major glycoproteins of 175 kDa and 105 kDa. None of the antibodies triggered peripheral blood lymphocytes or T cells to proliferation when tested under different culture conditions. All antibodies inhibited the proliferative response to concanavalin A or to allogeneic lymphocytes in mixed lymphocyte culture when whole IgG fractions were used. Complete inhibition of cytotoxic activity was obtained in cell-mediated lympholysis and in natural killer cell cytotoxicity (NK) when fresh peripheral blood lymphocytes were used as effector cells. Weak inhibition was also obtained in NK when mixed lymphocyte culture-activated effector cells were used. The inhibition was stronger, when NK activity was determined against MOLT4 target cells as compared to K562. Whereas F(ab')2 fragments of 873 IgG inhibited cytotoxic T lymphocyte activity completely, Fab fragments of 873 IgG neither inhibited proliferation nor cytotoxic T lymphocyte activity, but gave some inhibition of NK against MOLT4 targets. The results indicate that antibodies against these leucoagglutinin-reactive structures reacted with polypeptides similar to or identical with the human "leukocyte function-associated antigen-1" (LFA-1) considered to be an important mediator of cell-cell interactions and nonspecific adherence.