EARLY T-CELLS AND LATE T-CELLS - SUGGESTIVE EVIDENCE FOR 2 T-CELL LINEAGES WITH SEPARATE DEVELOPMENTAL PATHWAYS

Peripheral lymphocytes from mice were analyzed by a combination of cell electrophoresis and size distribution analysis, and the data were processed with a computer into 2-dimensional distribution patterns (fingerprints). The fingerprints of lymph node cells revealed the existence of at least 3 major classes of small lymphocytes. Cells with similar physical properties were found in the spleen and thoracic duct lymph. The data also allowed calculation of the quantitative ratios of the 3 cell types. In the normal mouse, the 2 electrophoretically faster cell classes represent essentially 2 subclasses of T [thymus-derived] cells. The quantitative ratios are here always in agreement with the known percentages of B [bone marrow-derived] and T cells. Lethally irradiated mice that were reconstituted with syngeneic bone marrow or fetal liver cells often lack one of the T cell subclasses. This has 2 important implications. It indicates that the widely used syngeneic or allogeneic bone marrow chimeras may be incomplete with respect to their T cell repertoire, and that experiments with these models should be interpreted with caution. The deficiency correlated strictly with a deficiency in a physically defined subset of small cortical thymocytes that was previously described. This correlation suggests that the fast peripheral T cells and the early small cortical thymocytes represent 2 developmental stages of a distinct cell lineage early T cell lineage, while the thymic pool of late small cortical thymocytes gives rise to electrophoretically slow peripheral T cells, which may be called late T cells. The possibility that both T cell lineages are derived from different classes of prethymic stem cells in the reconstituting stem cell preparation is discussed. The proportion of early T cells in the lymph nodes decreases with age. The ratio of late and early T cells is similar in the spleen and in the lymph nodes, and both cell classes contain a significant proportion of cells that are not affected by the early effects of adult thymectomy. They do not correspond to T1 and T2 cells.