HLA-B27 mediated expression of the α chain of the IL-2 receptor (CD25) as an activation marker on CD4+CD28- T cells. (a) Short term cell lines from HLA-B27 positive patients with ankylosing spondylitis were cross-linked to anti-CD3 directed immobilized antibodies (α CD3), incubated with HLA-B27 transfected C1R cells (C1R-B27) or untransfected cells (C1R) and controls, and exposed to antibodies directed against the NK receptors CD94 and CD158b/j (KIR2DL2/KIR2DL3/KIR2DS2), as indicated. (b) Fresh peripheral blood mononuclear cells were incubated together with anti-CD3 and HLA-B27 transfected T2 cells (T2-B27) or untransfected cells (T2) as indicated, harvested after 36 hours, and surface stained for CD4, CD28 and CD25. Whiskers box blots show the results of the independent experiments, with 50% of cases within the boxes and 80% between the end-points of the whiskers (lines). The two-sided paired t-test was used to determine statistical differences.