Immunosuppressive activity of IRA on the plaque-forming response to SRBC in vitro: reversal with educated cells.

The alpha-globulin-rich fraction of Cohn Fraction IV, designated IRA, suppresses the in vitro antibody response to sheep red blood cells (SRBC) without cytotoxicity. IRA was effective if added before or up to 24 hr after antigen exposure. The suppression could be reversed after 24-hr treatment by washing the cells two to three times; after 48 hr of IRA treatment, however, suppression could only be partially reversed. The addition of a population of thymus-derived cells educated to the antigen SRBC could effectively reverse the IRA-induced inhibition of antibody production, whereas BSA-educated T cells could not.