Ly49A-mediated inhibitory signals upon interaction with H-2D^d prevent the activation of CD4⁺ T cells.

Representative flow cytometric analysis of CTLA-4^−/− T cells from animals expressing the Ly49ATg in the presence and absence of the appropriate MHC class I compared to Ly49ATg⁻CTLA-4^−/− mice and littermate controls (3 weeks of age). Lymph node cells were incubated with the antibodies indicated and analyzed by flow cytometry as described.22 (A) Total lymph node T cells were stained for CD4 and CD8. (B) The expression of the indicated activation/memory cell surface markers on the CD4⁺ lymph node T cells from Ly49ATg⁺D^b CTLA-4^−/−, Ly49ATg⁻ H-2D^d CTLA-4^−/− and littermate control mice. The Ly49ATg⁺D^bCTLA-4^−/− T cells have an activated phenotype similar to that observed in Ly49ATg⁻ CTLA-4^−/− mice (data not shown; see also Chambers et al5). These results are representative of more than 10 independent experiments.