Activation of T and B thymus cells to recognize histocompatibility antigens

Lethally irradiated (A × CBA) F₁ or (A × C57BL/6) F₁ mice were injected with 10⁷ A strain thymus cells in attempts to activate donor cells to recognize CBA or C57BL/6 histocompatibility antigens, respectively. Activation could be revealed by injecting activated thymus cells (day 5 irradiated F₁ hybrid spleen cells) into corresponding unirradiated F₁ hybrid hosts. The alloantibody titers formed by these cells and the antirecognition structure (anti-RS) antibody titers induced by them were similar to those observed after injection of normal parental strain spleen cells, indicating that thymus cells had become endowed with recognition structures (RS). Alloantibodies, but no anti-RS antibodies, were present in the serum of F₁ mice given activated thymus cells treated with anti-θ and complement. It, therefore, appeared that activated thymus cells contained sufficient B cells differentiated into antibody-forming cells to give a measurable alloantibody response. On the other hand, receptors responsible for anti-RS antibody induction presumably were located on T cells. Specificity and restriction of antigenic recognition were revealed by negative results obtained when activated thymus cells were injected into F₁ hosts not containing the antigens against which activation had been directed.