Chicken thymocyte-specific antigen identified by monoclonal antibodies: ontogeny, tissue distribution and biochemical characterization

Two monoclonal antibodies, CT-1 (IgG1, kappa) and CT-1a (IgG3, kappa) were prepared against chicken thymocytes. The antigen identified by these antibodies was found to be a glycoprotein with a major polypeptide component having an apparent molecular weight of 63 000 and a minor polypeptide component of approximately 103 000. Immunoprecipitation and blocking experiments revealed that the two antibodies react with different antigenic determinants of the molecule. Ontogenic studies employing immunofluorescence failed to reveal the antigenic determinants on cells from the embryo or embryonic yolk sac on days 3 and 6 of incubation. The number of embryonic thymocytes bearing the molecules detected by these antibodies increased from 6% on day 12 to 54% on day 13; the frequency of thymocytes expressing this glycoprotein reached adult levels (greater than 90%) by the 15th day of embryonic age. In contrast, the CT-1 and CT-1a antibodies reacted with only 2-5% of blood and splenic cells and less than 0.05% of cells from bursa or bone marrow of young adult chickens. In the quail CT-1 reacted with cortical, but not medullary, thymocytes, while the CT-1a antibody was unreactive with quail thymocytes. The surface glycoproteins detected by these discriminating monoclonal antibodies may provide an important discriminating marker for thymic lymphocytes in the chicken and the quail.