Expression of Ly49A transgene in the presence of MHC class I H-2D^d prevents lymphocyte expansion in CTLA-4–deficient mice.

Single-cell suspensions of lymph node cells were prepared, counted, and analyzed for the expression of cell surface markers using antibodies specific for CD4, CD8, and TCRαβ. Absolute number of CD4⁺ in Ly49ATg⁺H-2^b/H-2^d, CTLA-4 wild-type and deficient animals. Each dot represents a single animal. Ly49ATg⁺H-2D^b: CTLA-4^+/+,+/−, n = 9; CTLA-4^−/−, n = 9; Ly49ATg⁺H-2D^d CTLA-4^+/+,+/−, n = 31; CTLA-4^−/−, n = 18. These animals were analyzed at 3 to 5 weeks of age, because the CTLA-4^−/− mice that develop the lymphoproliferative disease die by 4 weeks of age. The difference in the absolute CD4⁺ T-cell number in the CTLA-4^−/− mice expressing Ly49A transgene in the presence versus absence of the ligand H-2D^d was statistically significant (P < .001), whereas there was no statistically significant difference in the number of CD4⁺T cells between the Ly49ATg⁺ H-2D^d+CTLA-4^−/− and the littermate control mice.