The presence of concanavalin-A(Con-A)-like molecules on natural-killer (NK)-sensitive target cells: their possible role in swainsonine-augmented human NK cytotoxicity.

In the present study we examined the expression of concanavalin-A(Con-A)-like molecules on natural-killer (NK)-sensitive target cells and investigated their possible role in the human NK-cell phenomenon. The incubation of either peripheral-blood lymphocytes (PBL) or large granular lymphocytes (LGL) with swainsonine (SW), an inhibitor of mannosidase II, resulted in the augmentation of cytotoxicity against K562 leukemia cells. The enhanced cytotoxicity was associated with increased binding of fluorescein isothiocyanate-conjugated Con-A to SW-treated effector cells, and immunofluorescence staining of the target K562 cells using goat anti-Con-A antibody (Ab) showed a significant positive shift in the flow cytometric pattern. Electrophoretic separation and immunoblotting analysis revealed that 4 components with a molecular weight of approximately 95, 80, 60 and 50 kDa were recognized by anti-Con-A Ab from the detergent-extract of K562 cells. The addition of Con-A during the antibody incubation step of the Western blotting abolished their expression, thus excluding non-specific binding of the antibody. The addition of Con-A also strongly inhibited the cytotoxicity of SW-treated effector cells (PBL or LGL) against K562 cells, and this inhibition was abolished by 40 mM alpha-methyl-mannopyranoside (alpha-MM), which binds to Con-A. Furthermore, Con-A increased the binding frequency of SW-treated LGL to K562, in spite of the inhibited cytotoxicity, and this effect could be neutralized by the further addition of alpha-MM. Our results suggest that Con A-like molecules might play an important role in cell-cell interactions between SW-treated effector cells and NK target cells.