T-CELL DEVELOPMENT IN A MAJOR HISTOCOMPATIBILITY COMPLEX CLASS II-DEFICIENT PATIENT

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 thymoc ytes derived from a MHC class II-expressing thymus. Of these CD4+ CD8- BLS thymocytes, approximately only one third co-expressed the CD3 ant igen, moreover at a lower expression level when compared to control th ymocytes. This suggests a partial maturation of the CD4+ CD8- T cells in the absence of MHC class II expression. Among the BLS thymocytes, C D4+ CD8+ thymocytes could easily be detected. Noteworthy, the number o f 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 t he 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 c ell receptor (TcR) V gene family pool. However, the lack of detectable levels of thymic and peripheral MHC class Il antigen expression in th e BLS patient had altered the CD4-skewing patterns of TcR V gene famil ies which were present in normal individuals. In conclusion, the lack of MHC class II expression in the BLS patient does not completely inhi bit the CD4+ CD8- T cell development.