Differences in Ly 2- L3T4- thymocytes from foetal and adult murine thymus.
The thymus is the major site of mammalian T cell production. The exact steps which occur in the thymus and give rise to mature T cells have not been defined, but there is general agreement that the earliest T cells are included in the group of thymic lymphoid cells lacking Ly 2 (CD8) and L3T4 (CD4). This population represents 2-6% of adult thymocytes and the vast majority of thymocytes in the mouse embryo until about day 16 of gestation. It has often been assumed that the foetal and adult CD4- CD8- thymocytes are equivalent. This paper shows that there are significant differences between the CD4- CD8- cells from these sources, in that the adult includes at least two subsets which are undetectable in the embryo. These two subsets of CD4- CD8- cells are both Ly 1high, B2A2- and M1/69-; one is Thy 1+ and one is Thy 1-. Each represents 20-25% of adult CBA double negative thymocytes. Both these populations are excluded from analyses of CD4- CD8- thymocytes which have been further selected as Ly 1low, a procedure adopted in several studies of early thymocytes. Even those subpopulations of CD4- CD8- cells which appear to express similar markers in adult and embryo thymus are quite different when analysed for cell size (forward light scatter), with the embryonic forms being much larger.
D000367:Age Factors; D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly; D000954:Antigens, Surface; D005333:Fetus / Q000166:cytology*; D051379:Mice; D008808:Mice, Inbred CBA; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology* / Q000276:immunology; D018800:Thy-1 Antigens; D013950:Thymus Gland / Q000166:cytology*
D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly; D000954:Antigens, Surface; D018800:Thy-1 Antigens