Lectin-induced suppression of antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood mononuclear cells.

Incubation of human peripheral blood mononuclear cells in the presence of 25 mg/l concanavalin A (Con A) or 2 mg/l phytohaemagglutinin (PHA) suppressed their ADCC activity. Thirty-minute incubation with the mitogens resulted in a significant decrease in ADCC activity. The effect was more striking with longer (24 and 48 h) incubation. The suppressive effect of PHA was abolished after 6 days incubation, while no such phenomenon was observed with Con A. Macrophages participating in the ADCC reaction were not influenced by the lectin treatment, though their removal increased the suppressive effect. The lectin-induced suppression of ADCC activity did not correlate with the suppression of Con A-induced blastogenesis. The suppressive effect of lectins on ADCC is not mediated through suppressor cells, but rather represents a direct action of ligands on the (killer) lymphocyte membranes, resulting probably in an altered metabolism, or inhibition of membrane mobility or lymphocyte locomotion.