Inhibition of human lymphocyte transformation by tomato lectin

The lectin from tomato (Lycopersicon esculentum) fruits was found to be non-mitogenic for human lymphocytes in culture and actually suppressed spontaneous DNA synthesis. It also inhibited the transformation of human peripheral blood lymphocytes induced by recall antigens or allogeneic cells in vitro. This inhibition was most effective when the lectin was present from the beginning of the culture period, and could be abolished by the simultaneous addition of oligomers of N-acetylglucosamine. The tomato lectin was able to bind to several major lymphocyte cell surface glycoproteins, but not to the major histocompatibility (HLA) antigens. The binding of tomato lectin to lymphocytes could be inhibited by wheat germ agglutinin (WGA), but not by concanavalin A. Tomato lectin could agglutinate monocytes and B lymphocytes as well as T lymphocytes. Human serum used to supplement the culture medium supporting lymphocyte transformation was equally effective after passage through a tomato lectin-Sepharose column. The inhibition of lymphocyte transformation brought about by tomato lectin was not stopped by exogenously added interleukin 1 and/or interleukin 2, even at very high concentrations.