In addition, we compared IL-2 production by CD4+ T cells after CD3 and CD28 costimulation in the presence of IL-10 in active RA patients and in healthy controls. Similarly, IL-2 production was not affected by 1 ng/ml IL-10 in RA patients (percentage decrease, -2.1 ± 13.8%), while it was significantly reduced in healthy controls (61.1 ± 13.7%; P < 0.05). Taken together, these results indicate that RA CD4+ T cells become less susceptible to the immunoregulatory effect of IL-10 during the active phase.