The effect of constitutive CD8 expression on thymic selection; implications for the mechanism of CD4 and CD8 lineage commitment.
The choice of an immature T cell to become a CD4 cell or a CD8 cell may be the result of instructive signals generated during positive selection. Alternatively, the initial commitment to a CD4 or CD8 lineage may be made independently of the specificity of the TCR. In this article, I describe our efforts to test the latter possibility using mice expressing a constitutive CD8 transgene. If lineage commitment is initially independent of MHC specificity, expression of ectopic CD8 in CD4 cells should allow CD4 cells with class I specific TCR to mature. We find that although some mature class I specific CD4 cells can be detected in CD8 transgenic mice, they are a minor population compared to class I selected CD8 cells. The implications of these results for the mechanism of lineage commitment are discussed.
Robey
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Department of Molecular and cell Biology, University of California, Berkeley 94720.
D000818:Animals; D015704:CD4 Antigens / Q000096:biosynthesis*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D016827:CD8 Antigens / Q000096:biosynthesis*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D017637:Clonal Deletion / Q000276:immunology*; D006649:Histocompatibility Antigens / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D018448:Models, Immunological; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology*
D015704:CD4 Antigens; D016827:CD8 Antigens; D006649:Histocompatibility Antigens; D011948:Receptors, Antigen, T-Cell