Pokeweed mitogen inhibition of protein synthesis in cultured lymphoblastoid lines

Pokeweed mitogen (PWM) and ricin are both lectins derived from plant seeds. They are glycoproteins and share the ability to agglutinate a variety of animal cells including erythrocytes. The effect of these two lectins on protein synthesis was studied in four long-term lymphoblastoid lines (8866 and GM1531, which are B cell lines; and CCRF/CEM and MOLT 4, which are T-cell lines). Ricin (50 micrograms/ml) completely inhibited protein synthesis by 2 hr in both B-cell and T-cell lines as measured by the uptake to [3H]leucine. The PWM appeared more specific and at a concentration of 500 micrograms/ml inhibited protein synthesis only in B-cell lines (8866 and GM1531). This effect was maximal at 5 hr. To investigate the reason for the differential effect of PWM on T and B cells, 125I-labeled PWM was incubated with 8866, MOLT 4, and CCRF/CEM to see if a significant difference in binding to B cells and T cells could be demonstrated. It does not appear that differential effect on T and B cells is due to a difference in the amount of PWM bound. On the other hand it is possible that the B cells may bind some toxic subcomponent of the PWM preparation that the T cells do no bind because of a difference in composition or arrangement of cell surface glycoproteins.