SPECIFICITY OF NONSPECIFIC CONCANAVALIN A-INDUCED HELPER FACTORS

Addition of supernatants from concanavalin (Con) A-stimulated spleen cells enable nude spleen cells to respond in vitro to a variety of antigens (sheep (SRBC) and horse erythrocytes (HRBC)). Experiments presented here, indicate that such nonspecific helper supernatants are in fact a polyclonal mixture of diverse, specific activities. Con A stimulation of thoracic duct lymphocytes, specifically depleted of SRBC or HRBC-reactive cells by the Sprent technique, results in a specific decrease in the activity to the relevant antigen. Con A stimulation of in vivo activated thymocytes results in the production of helper supernatants which are almost totally specific for the antigen used in priming. In spite of these indications of specificity, it has been impossible to absorb out helper activity from normal Con A supernatants on the corresponding antigen. Specific removal of helper activity can readily be achieved by absorbing helper supernatants on complexes of antigen and early immune sera. Various control experiments demonstrated that the loss of activity in the absorbed supernatants was not due to carry-over of antibody into the test cultures. The fraction of helper activity that can be specifically removed on antigen-antibody complexes depended on the conditions used in the preparation of the supernatants. This fraction was highest when Con A activation of T [thymus-derived] cells was performed in the presence of B [bone marrow-derived] cells without antigen. Nonspecific helper factors are apparently a mixture of diverse molecules, some of which show specificity for variable regions of antibodies.