The value of rheumatoid factor and anti-citrullinated protein antibodies as predictors of response to infliximab in rheumatoid arthritis: an exploratory study

Methods. A total of 101 active RA patients were prospectively treated with infliximab (3 mg/kg). Changes in disease activity were monitored by the 28-joint DAS (DAS-28). Serum levels of different isotypes [immunoglobulins M, G and A (IgM, IgG and IgA)] of RF and anti-citrullinated peptide antibodies were measured by ELISA. Results. The mean DAS-28 decreased from 5.9 (1.1) at baseline to 4.0 (1.3) at Week 16 of infliximab treatment (P < 0.001). High baseline levels of different isotypes of RF (all P < 0.008), ACPA IgM (P = 0.008) and ACPA IgG (P = 0.07) were associated with an absolute decrease in DAS-28 after TNF blockade. This relationship persisted after adjusting for DAS-28 at baseline. However, the different isotypes of baseline RF and ACPA levels accounted for only a small proportion of variance in treatment response (RF: R-2 between 7 and 12% and ACPA: R-2 between 4 and 7%). The simultaneous presence of all three isotypes of RF or ACPA had no additive value. Conclusion. Presence as well as the titres of RF and IgM ACPA at baseline are significantly correlated with better response to infliximab treatment. However, this correlation is not strong enough to allow a reliable prediction in individual patients.