Potentiation of specific human in vitro immune responses by the Fc portion of human immunoglobulin.

Fc fragments derived from a human IgG1 myeloma protein were found to be a potent adjuvant for in vitro human immune responses. The addition of Fc to cultures of human PBL along with SRBC resulted in a pronounced enhancement of the primary in vitro anti-SRBC response. In addition to potentiating the humoral immune response, Fc was also found to augment the tetanus toxoid-induced T cell proliferative response. Augmentation of the immune response is mediated by Fc and not the result of an artifact due to the addition of extraneous protein to culture because neither intact IgG1 nor Fab fragments derived from this myeloma protein possessed any adjuvant properties. The temporal relationship of the administration of antigen and Fc to culture is critical for the potentiation of the immune response. The maximal Fc adjuvant effect was observed when Fc was added with antigen at the beginning of culture.