Enhancement of humoral immune responses. I. Potentiating influence of purified protein derivative on the invitro immune response of spleen cells sensitized to Mycobacterium bovis and Mycobacterium avium.

Addition of purified protein derivate (PPD) to suspension cultures of spleen cells from swine sensitized to Mycobacterium bovis and Mycobacterium avium resulted in marked enhancement of antisheep erythrocyte plaque-forming cells after stimulation with sheep erythrocytes. The enhancing effect appeared early in the response and was specific for the sensitizing antigen. The enhancing effect was dependent upon the presence of both sheep erythrocytes and PPD in the culture system. PPD had no effect in the absence of sheep erythrocytes. Addition of PPD to cells from nonsensitized animals did not produce any enhancing effect.