期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1993
卷号：90
期号：7
页码：2779-2783
DOI：10.1073/pnas.90.7.2779
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Generation of immunocompetent alpha/beta T-cell receptor-positive T cells from CD4+CD8+ thymocytes depends upon their interaction with thymic major histocompatibility complex (MHC) molecules. This process of positive selection provides mature T cells that can recognize antigens in the context of self-MHC proteins. Previous studies investigating haplotype restriction in thymic and bone-marrow chimeras concluded that radioresistant thymic cortical epithelium directs the positive selection of thymocytes. There is controversy, however, as to whether intra- or extrathymic radiosensitive bone marrow-derived macrophage and dendritic cells also can mediate positive selection. To determine whether CD4+ T cells can be positively selected by hematopoietic cells, we generated chimeric animals expressing MHC class II molecules on either bone marrow-derived or thymic stromal cells by using a recently produced strain of MHC class II-deficient mice. CD4+ T cells developed only when class II MHC molecules were expressed on radioresistant thymic cells. In contrast to what recently has been observed for the selection of CD8+ T lymphocytes, MHC class II-positive bone marrow-derived cells were unable to mediate the selection of CD4+ T cells when the thymic epithelium lacked MHC class II expression. These data suggest that CD4+ and CD8+ T cells may be generated by overlapping, but not identical, mechanisms.
