Comparison of the suppressive effects of RA SF cells on the anti-CD3/CD28-induced and alloantigen-induced proliferation of autologous T cells. (A) Isotope incorporation (cpm) by anti-CD3/CD28 Ab-stimulated PBMCs (light blue bar) was moderately, but significantly reduced in the presence (dark blue bar) of SF cells (SFC) from 3 RA patients (RA #7, 8, 9). (B) Allogeneic PBMC-induced proliferation of PBMCs from the same 3 patients (orange bar) was greatly reduced in the presence of autologous SF cells (dark red bar). The data shown in panels A and B are the means ± SEM of background-corrected cpm values (4 wells per condition) (*p < 0.05, **p < 0.01; Paired t test). (C) Comparison of the ratios of anti-CD3/CD28-induced (dark blue bar) and allogeneic PBMC-induced (dark red bar) proliferation of RA PBMCs in the presence of autologous SFC in the 3 RA patients (cpm values shown in panels A and B) indicated that SF cells from the same patients were more efficient in suppressing the allogeneic PBMC-induced than the anti-CD3/CD28-induced proliferation of autologous T cells. The data are the means ± SEM of background-corrected proliferation ratios (*p < 0.05; Paired t test).