Regulation by antibody of phytolectin induced lymphocyte proliferation. I. Evidence for two mechanisms of suppression

Studies were conducted to determine the mechanisms of antibody suppression of phytohemagglutinin (PHA)- and concanavalin A (Con A)-induced lymphocyte proliferation. Initial experiments incubated lymphocytes with either PHA or Con A, and at various times the respective anti-phytolectin was added to the cultures. DNA synthesis was less than 20% of the total response if anti-PHA was added within 2 hr and if anti-Con A was added within 10 hr of addition of mitogens to the culture. At the concentrations used, anti-PHA reduced PHA binding to the lymphocytes, while anti-Con A did not reduce Con A binding to the cells. Antibody was non-toxic and specific for its respective mitogen. Additional experiments incubated lymphocytes with either PHA or Con A and then the cells were washed and placed in mitogen-free media. The addition of antibody to cultures which had been washed markedly suppressed proliferation. Using radiolabeled PHA and Con A in one group of experiments and fluorescent labeled anti-mitogen antibodies in others, it was determined that antibody did not remove Con A or PHA from the cell, but instead antibody slowed the release of mitogen from the lymphocyte. Anti-mitogen antibody remained attached to mitogen on the surface of lymphocytes for at least 24 hr. The experiments suggest that antibody can suppress the lymphocyte reaction by blocking the necessary phytolectinlymphocyte interaction and interrupting stimulation by cell-bound mitogen.