Serological Analysis of Thymus and Spleen

Thymic lymphocytes are continuously replaced by stem cells entering the thymus. The thymus of animals receiving lethal total body irradiation, followed by administration of bone marrow or spleen cells, is repopulated by cells derived from the inoculure (1-6). Similarly, repopulation of the unirradiated thymus eventually occurs in animals in which only the lower third of the body was irradiated prior to bone marrow administration (7). The thymus of mice (8) or of chicken embryos (9) joined by parabiosis contains cells derived from the partner. Analysis of thymus grafts has shown that the lymphoid elements are replaced by cells derived from the host (10-12). Thymic lymphocytes constantly display distinctive serological properties (see references 12 and 14) in spite of their replacement by the continuous entry of stem cells. Thymus cells of all strains of mice show a distinctive sensitivity to the cytotoxic effect of guinea pig serum (GPS) (15-19). The thymus cells of some strains of mice, such as the A strain, possess a thymus-specific antigen, the TL (thymus-leukemia) antigen, while other strains of mice, such as the C57BL strain, do not have this antigen on their thymus cells (20, 21).