The anti-inflammatory effect of abatacept is most pronounced in patients with high-titer autoantibodies (including anticitrullinated protein antibodies [ACPA] and rheumatoid factor [RF]). Considering that autoantibodies trigger inflammatory cytokine production by monocytes and that abatacept binds to monocytes, influencing their functional state, we hypothesized that abatacept may effectively inhibit the production of several different cytokines by ACPA- or RF-challenged monocytes.
Peripheral blood CD68
Exposure to ACPA or RF significantly induced the production of TNF-α (20-fold and 27-fold, respectively), IL-1β (each 4-fold), IL-6 (12-fold and 11-fold, respectively), IL-8 (43-fold and 30-fold, respectively), and CCL2 (each 4-fold) in human monocytes. Abatacept inhibited this autoantibody-mediated upregulation of cytokines, reducing TNF-α by > 75%, IL-1β by > 65%, IL-6 and IL-8 by > 80%, and CCL2 by > 60%. In contrast, a TNF inhibitor did not influence autoantibody-induced proinflammatory cytokine production. IDO inhibition reversed the effect of abatacept and again permitted the induction of cytokine production by ACPA and RF.
These data show that abatacept interferes with autoantibody-mediated cytokine production by monocytes through induction of IDO. This inhibitory effect on the production of several effector cytokines in RA may explain the fast anti-inflammatory effect of abatacept as well as its preferential efficacy in patients with high-titer ACPA and RF.