Signaling through the LFA-1 leucocyte integrin actively regulates intercellular adhesion and tumor necrosis factor-alpha production in natural killer cells.

The LFA-1 leucocyte integrin is known to participate in natural killer (NK) cytolytic activity, mediating effector target interactions. The possibility that LFA-1 may also play an active regulatory role in NK cells has been explored. To this end, we have employed a monoclonal antibody (HP1N) raised against recombinant interleukin-2 (rIL-2)-activated NK cells, which recognizes the alpha chain of the LFA-1 heterodimer (CD11a). In contrast to other anti-CD11a mAb the HP1N and its F(ab')2 fragment did not affect NK cell-mediated cytotoxicity and triggered a strong homotypic adhesion of NK cells and other LFA-1+ cells. Cellular aggregation was inhibited by anti-CD18 mAb, anti-ICAM-1 mAb, and other anti-CD11a mAb. Remarkably, the HP1N mAb was also shown to induce tumor necrosis factor-alpha (TNF-alpha) production from NK cells upon costimulation with anti-CD16 mAb. Such an effect appeared to be independent from homotypic adhesion since it took place in Mg(2+)-free medium, where NK cell aggregation was inhibited. Moreover, incubation with the HP1N mAb triggered a Ca2+ influx into the cytosol; this effect was clearly observed upon cross-linking of cell bound HP1N and was also substantiated with other anti LFA-1 (CD11a and CD18) mAb. Taken together these results indicate that the LFA-1 molecule is capable of transducing signals in NK cells, which regulate the intercellular interaction with its ligand, and enhance the activation via Fc gamma receptor type III.