Adult thymectomy does not alter the proportion of T cells of the Ly 123 subclass

Abstract

The murine T cell antigens Ly 1, 2 and 3 have been useful in defining functionally distinct T cell subpopulations1. However, the relationship between Ly 123+ cells and Ly 1+23− cells is not clear2–4 It has been claimed5,6 that all cells leaving the thymus are Ly 123+ the implication being that these must be the precursors of Ly 1+23− cells and that maturation involves the loss of Ly 2 post-thymically. Previous work has shown a 50% drop in the proportion of T cells of the Ly 123+ subclass following adult thymectomy5. The interpretation was that the Ly 123+ cells differentiated into Ly 1+23− cells and that no Ly 123+ migrants from the thymus were replacing them. However, when we directly measured the Ly phenotype of migrant cells within a few hours of their exit from the thymus7, we found they were mature in phenotype and already contained Ly 1+23− cells in the same proportion (∼60%)8 as peripheral T cells. This result suggests that adult thymectomy should not affect the subclass distribution of T cells. We have therefore repeated the adult thymectomy experiments using more precise techniques (flow cytometry and monoclonal antibodies) and the results reported here, in contrast to those of the earlier study5, did not show any change in the proportion of Ly 123+ cells after adult thymectomy, even though total T cell numbers were substantially reduced.