Lymphokine-activated cell-associated antigen involved in broad-reactive killer cell-mediated cytotoxicity.

Spleen cells from rats which had been hyperimmunized with mouse lymphokine-activated killer (LAK) cells, were fused with the mouse myeloma cell line, P3 X 63 Ag8.653. Antibodies secreted by 1500 cultures were selected by their blocking effect on LAK cell-mediated cytotoxicity in the absence of complement. Two monoclonal antibodies (KBA4 and KBA6) greatly inhibited the cytotoxic activity of LAK cells, which were induced from mouse spleen cells by culture with recombinant human interleukin 2 (r-IL-2). These antibodies also blocked the cytotoxic activity of natural killer (NK) cells, but activated macrophages (A-M phi) were only slightly sensitive to them. However, no effect of the antibodies on the cytotoxic activity of cytotoxic T lymphocytes (CTL) was detected. These data suggest that the specific antigen, lymphokine-activated cell-associated (LAA) antigen, defined by these monoclonal antibodies may be associated with the recognition mechanisms of broad-reactive killer (BRK) cell-mediated cytotoxicity. The observation that low levels of LAA antigen are distributed in all lymphoid cells and that it was significantly enhanced by treatment of the cells with r-IL-2 suggests that the antigen may be involved in lymphocyte-activation mechanisms. We also found that the LAA antigen consists of two distinct polypeptides with Mr of 180,000 and 95,000 Da, which are similar to that of LFA 1 antigen. However, the biological characteristics of LAA antigen did not coincide with those of LFA 1. Therefore, KBA MAb may recognize a carbohydrate epitope distinct from that of LFA 1.