Immunogenic function of macrophages: In vitro production of antibodies to a hapten-carrier conjugate

Spleens of mice which had been immunized with rabbit serum albumin (RSA) respond to an in vitro challenge with dinitrophenyl (DNP)-RSA, by the production of anti-DNP antibodies. This "carrier-effect" was produced only if immunization with RSA was carried out in complete Freund's adjuvant. We found, however, that the adjuvant treatment could be substituted by immunizing with peritoneal macrophages (PEC) which had interacted with RSA. The same result was obtained when immunization with PEC-RSA was carried out in X-irradiated animals reconstituted with thymus and bone marrow cells. To determine what is the target cell for the action of the macrophage-antigen complex, X-irradiated animals were treated first with thymus and PEC antigen complex and 8 days later with bone marrow cells, or first with bone marrow and PEC antigen, and then with thymus cells. Only the spleens of the first group responded in vitro to DNP-RSA conjugate. It is therefore deduced that production of antibodies to DNP-RSA involves cooperation of at least three cell types. The macrophage-antigen complex interacts first with T-cells, prior to involvement of bone marrow precursors of antibody-producing cells.