Positive selection of a T-cell subpopulation in the thymus in which it develops.

In SWR mice the expression with high-density V beta 17a (high V beta 17a) of the T-cell antigen receptors correlates with the CD4+8- subpopulation of thymocytes. By contrast, in thymocytes of SJL mice the expression of high V beta 17a is observed on the CD4+8- or CD4-8+ subpopulation. However, when the thymocytes from SWR mice have been developed in the SJL or B10 thymus but not in the H-2 compatible DBA/1 thymus, a greater proportion of thymocytes that express high V beta 17a was found to be CD4-8+. By contrast, only a small proportion of KJ23a+ thymocytes from SJL mice that had differentiated in the thymus of SWR or DBA/1 mice was CD4-8+, whereas a high proportion of CD4+8- cells expressed V beta 17a. Further, an intermediate proportion of KJ23a+ thymocytes that had derived from SJL donor mice was present on CD4-8+ thymocytes that had developed in B10.A(4R) thymus. These findings demonstrate that the appearance of a particular subpopulation of thymocytes (CD4-8+ with a beta chain of T-cell antigen receptor identified as V beta 17a) is determined by the histocompatibility complex products that are expressed in the thymic microenvironment in which the T cells develop.