Abstract
Extracts of Maclura pomifera seeds (MP-Ext), which agglutinate leukocytes and erythrocytes of rats and other animals, were labeled with 125I. Labeled extracts were adsorbed to rat cells and eluted (125I-MP) by an excess of D-melibiose, a known inhibitor of the binding of seed extracts. Over 80% of 125I-MP bound to rat cells. Binding was inhibited by carbohydrates related structurally to D-melibiose but not by lactose, glucose, or carbohydrates unrelated to D-melibiose. Thymus cells bound larger quantities of 125I-MP than cells of spleen, bone marrow, or erythrocytes and binding by spleen cells from thymectomized animals was reduced. Thymus cells were also selectively stained by fluor-labeled MP-Ext. 125I-MP, phytohemagglutin, and concanavalin A (Con A) were found to recognize distinct receptors on BN rat cells since they did not compete in binding tests and since they are inhibited by different carbohydrates. Eluted MP was mitogenic for spleen cells in serum-free medium, but not in medium containing serum. In addition, it augmented the mitogenic effects of Con A.
