Suppression of anti-CD3/CD28-induced polyclonal proliferation of autologous peripheral blood T cells by RA SF cells. (A) Peripheral blood mononuclear cells (PBMC) stimulated with anti-CD3/CD28 monoclonal antibodies (Abs) were cultured in the absence (condition “a”) or presence (“b”) of SF cells (SFC) from the same RA patient (RA #3). Background controls included PBMCs cultured without anti-CD3/CD28 Abs (“c”) and SF cells cultured with anti-CD3/CD28 Abs (“d”). The results shown are the means ± SEM of isotope incorporation (counts per minute, cpm) by the proliferating cells (6 wells per condition). As the actual cpm values at all of the listed conditions varied from patient to patient, we calculated the proliferation ratio (with background correction) for each RA patient using the formula: [b − (c + d)]/(a − c), where the positive control (a - c) was set to 1. (B) As indicated by the proliferation ratios, the anti-CD3/CD28-induced proliferation of autologous PBMCs (light gray bar) was significantly suppressed in the presence of SF cells (black bar). The results shown are the means ± SEM of background-corrected proliferation ratios (**p < 0.01; Wilcoxon matched-pair signed rank test; n = 9 patients).