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Elimination In Vivo of Developing T Cells by Natural Killer Cells
Address correspondence to Hidde L. Ploegh, Dept. of Pathology, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115. Phone: (617) 432-4777; Fax: (617) 432-4775; email: ploegh{at}hms.harvard.edu
Natural killer cells gauge the absence of self class I MHC on susceptible target cells by means of inhibitory receptors such as members of the Ly49 family. To initiate killing by natural killer cells, a lack of inhibitory signals must be accompanied by the presence of activating ligands on the target cell. Although natural killer cell–mediated rejection of class I MHC–deficient bone marrow (BM) grafts is a matter of record, little is known about the targeting in vivo of specific cellular subsets by natural killer cells. We show here that development of class I MHC–negative thymocytes is delayed as a result of natural killer cell toxicity after grafting of a class I MHC–positive host with class I MHC–negative BM. Double positive thymocytes that persist in the presence of natural killer cells display an unusual T cell receptor–deficient phenotype, yet nevertheless give rise to single positive thymocytes and yield mature class I MHC–deficient lymphocytes that accumulate in the class I MHC–positive host. The resulting class I MHC–deficient CD8 T cells are functional and upon activation remain susceptible to natural killer cell toxicity in vivo. Reconstitution of class I MHC–deficient BM precursors with H2-Kb by retroviral transduction fully restores normal thymic development.
Key Words: thymocyte development • bone marrow chimera • NK cell toxicity • CD8 T cells • retroviral infection
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