Origin and fate of a thymocyte-specific antigen.

The incidence of a thymocyte-specific antigen in thymuses of rats at different ages was studied by immunofluorescence using an anti-thymus microsome serum. This serum, which could detect an antigen common to all lymphocytes, was made thymus-specific by absorption with non-thymic lymphoid organs. The thymic antigen was detected in the earliest embryo (32 mm) in which lymphoid cells are recognizable in the thymic anlage, where it appeared to be present in all thymic lymphocytes. With increasing age, both the proportion of lymphoid cells bearing the antigen and the amount of antigen present were decreased. In lethally irradiated marrow-injected animals, the thymus recovered its normal histology and lymphoid antigenicity within a month, but the thymocyte-specific antigen did not reappear. The findings suggest that the antigen is an exclusive component of native thymic lymphocytes.