Two distinct antigenic markers for rat thymus and T cells defined by monoclonal antibodies.

Rat thymus and T-cell antigens were defined by using two distinct monoclonal antibodies (R-1-3B3 and R-1-12C5). R-1-3B3 antibody, when tested for its reactivity with rat lymphoid cells by immunofluorescence, labelled virtually all thymus and T cells but not B cells and bone marrow cells. The antigen defined by this R-1-3B3 antibody occurred more abundantly on medullary thymocytes and peripheral T cells than on cortical thymocytes. Immunochemical data showed that R-1-3B3 antibody recognized a single glycoprotein with a molecular weight of 67,000, which were able to interact with Lens culinaris haemagglutinin. R-1-12C5 antibody, on the other hand, reacted with all of thymus and T cells as well as with a subpopulation (approximately 20%) of bone marrow cells. In contrast to the antigen defined by R-1-3B3, that detected by R-1-12C5 antibody existed largely on cortical thymocytes and to a much lesser extent on medullary thymocytes and peripheral T cells. R-1-12C5 antibody detected a single glycoprotein with a 95,000 molecular weight, which could also interact with Lens culinaris haemagglutinin. Based on these data described above and since both antigens defined by R-1-3B3 and R-1-12C5 antibodies were absent from rat brain tissue, we concluded that they were distinct from brain-associated thymic antigens in rats including Thy-1 and W3/13 antigen systems.