Stimulation of human lymphocytes by galactose-specific abrus and ricinus lectins.

Human lymphocyte cultures were incubated with the nontoxic abrus agglutinin and with ricin B chain, and the incorporation of 3H thymidine was measured. Abrus agglutinin stimulated strongly the thymidine incorporation whereas ricin B chain had a much lesser effect. When galactose or lactose was added to the cultures together with the lectins, the abrus agglutinin and ricin B chain induced thymidine incorporation was strongly reduced. There was a linear relationship between the concentration of lectin and the concentration of lactose required for inhibition of lymphocyte stimulation. N-acetyl-galactosamine had a much lesser inhibiting effect and alpha-methyl-mannoside did not cause any inhibition. The abrus agglutinin induced thymidine incorporation was not demonstrable before 36 to 40 hr and reached its maximum after 2 to 5 days. If lactose was added within the first 4 hr of incubation with abrus agglutinin no stimulation was observed.