Involvement of LFA-1 in hepatic NK cell (pit cell)-mediated cytolysis and apoptosis of colon carcinoma cells

Background/Aims: Previous studies have shown that hepatic natural killer (N K) cells, also called pit cells, have a higher cytotoxicity against certain tumor cells and have a higher expression of the cell adhesion molecule CD1 1a as compared with blood NK cells, We further investigated the involvement of the adhesion molecules, reported to be involved in target cell killing by blood NK cells, in pit cell-mediated colon carcinoma cell killing, Methods: Cr-51-release and DNA fragmentation were used to quantify target c ell lysis and apoptosis, respectively, Adhesion of pit cells to CC531s mono layers was quantitated, Results: Flow cytometric analysis showed that pit cells expressed CD2, CD11 a, CD18 and CD54, CC531s cells expressed only CD54. Treatment of freshly is olated pit cells with monoclonal antibodies (mAbs) to CD11a and CD18 inhibi ted not only the pit cell-mediated CC531s cytolysis but also the pit cell-i nduced apoptosis of CC531s cells, The combination of mAbs to CD11a, CD18 an d CD54 further increased the inhibition of pit cell-mediated CC531s cytolys is and apoptosis, Anti-CD2 mAb did not affect these processes, The binding of pit cells to CC531s cells was also inhibited by anti-CD11a, and CD18 mAb s, but not by anti-CD2 mAb. Anti-CD54 mAb reduced the target cell killing a nd the binding only slightly, Conclusions: These results indicate that CD11a/CD18 (LFA-1) present on pit cells plays an important role in pit cell-mediated target cell adhesion, ly sis and apoptosis, This finding might explain why pit cells, which have a h igher expression of LFA-1 as compared to blood NK cells, are more cytotoxic against tumor cells as compared to blood NX cells.