Phenotypic characterization of CD4+CD28- T cells. (a) Surface staining of CD4+ T cells was performed using monoclonal antibodies directed against the natural killer cell marker CD57 and the lymphocyte marker CD7 (n = 7). (b) Further staining was performed using the specific antibodies directed against the natural killer cell immunoglobulin-like receptors CD158a/h (KIR2DL1/KIR2DS1), CD158b/j (KIR2DL2/KIR2DL3/KIR2DS2) and NKB1 and the C-type lectin receptor CD94. Whiskers box blots show the results of 11 independent experiments, with 50% of cases within the boxes and 80% between the end-points of the whiskers (lines). The Wilcoxon test was used to determine statistical differences.