T cell development in a major histocompatibility complex class II‐deficient patient

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Abstract
In this report we show that the major histocompatibility complex (MHC) class II‐negative thymus of a bare lymphocyte syndrome (BLS) patient contains a reduced CD4+ CD8− T cell population when compared to thymocytes derived from a MHC class II‐expressing thymus. Of these CD4+ CD8− BLS thymocytes, approximately only one third co‐expressed the CD3 antigen, moreover at a lower expression level when compared to control thymocytes. This suggests a partial maturation of the CD4+ CD8− T cells in the absence of MHC class II expression. Among the BLS thymocytes, CD4+ CD8+ thymocytes could easily be detected. Noteworthy, the number of CD4− CD8+ thymocytes was significantly increased. CD4+ CD8− T cells could also be found among the BLS peripheral blood mononuclear cells, albeit at reduced numbers. Despite the absence of peripheral MHC class II expression, the majority of these CD4+ CD8− T cells co‐expressed the CD45RO marker. In the BLS patient, thymocytes as well as peripheral CD4+ CD8− T cells were not restricted in the use of the available T cell receptor (TcR) V gene family pool. However, the lack of detectable levels of thymic and peripheral MHC class II antigen expression in the BLS patient had altered the CD4−skewing patterns of TcR V gene families which were present in normal individuals. In conclusion, the lack of MHC class II expression in the BLS patient does not completely inhibit the CD4+ CD8− T cell development.