Restrictive IgG antibody response against mutated citrullinated vimentin predicts response to rituximab in patients with rheumatoid arthritis

Abstract

Introduction: Antibodies against mutated citrullinated vimentin (AMCV) represent a useful diagnostic marker with correlation to disease activity in patients with rheumatoid arthritis (RA). Since seropositivity for citrullinated autoantibodies was predictive for response to B-cell depleting therapy (BCDT) with rituximab (RTX), we investigated whether differences in antibody fine reactivity and immunoglobulin (Ig) isotype kinetics among AMCV-positive patients could provide additional information about outcome.

Methods: A total of 50 AMCV IgG-positive RA patients (RTX responders (RRs) n = 37 and non-responders (NRRs) n = 13) were analyzed for reactivity against MCV epitopes and co-existent AMCV isotypes IgM and IgA. Antibody titers were determined by enzyme-linked immunosorbent assay at baseline and 24 weeks after the first cycle of RTX, and compared to kinetics of rheumatoid factor (RF) and antibodies against cyclic citrullinated peptide (ACCP).

Results: Recognized MCV epitopes by AMCV IgG of RRs and NRRs showed similar baseline patterns, with reducing reactivity in RRs and unchanged or even expanding reactivity in NRRs upon RTX treatment. At baseline, RRs were more frequently negative for AMCV subtypes, especially for IgA (68%), compared to NRRs (31%). Being AMCV IgA-negative at baseline indicated a good treatment response to RTX (negative predictive value = 0.86). Co-existence of AMCV IgA and IgG with stable titers upon treatment were associated with poorer responses to RTX. Furthermore, reductions of AMCV IgA levels upon RTX correlated with the improvement of 28-joint Disease Activity Score (DAS28). In comparison, subtypes of RF and ACCP were not of additional value for prediction of RTX response.

Conclusions: Restrictive IgG seropositivity against MCV with treatment-associated decline in fine reactivity and titers was predictive for response to RTX. Double-positivity for AMCV IgG and IgA was associated with failure to respond to BCDT, suggesting a pathogenetic and less sensitive IgA-producing B-cell subset in NRRs.

Fig. 1

MCV epitope mapping in responders to RTX. The pattern of recognized MCV epitopes by IgG anti-MCV antibodies (AMCV) of RTX responders (n = 23) were reduced from baseline (a) to 24 weeks (b) after RTX treatment (x axis: wells A to H; y axis: wells 1 to 12; z axis: number of positive patients)

Fig. 2

MCV epitope mapping in non-responders to RTX. The pattern of recognized MCV epitopes by IgG anti-MCV antibodies (AMCV) of RTX non-responders (n = 11) remained stable or even expanded from baseline (a) to 24 weeks (b) after RTX treatment (x axis: wells A to H; y axis: wells 1 to 12; z axis: number of positive patients)

Fig. 3

Baseline autoantibody profiles of responders and non-responders to RTX. Non-responders (blue) more frequently showed IgA and IgM antibodies against MCV (AMCV) than responders (red), whereas the antibody distribution of rheumatoid factor (RF) and antibodies against cyclic citrullinated peptide was nearly similar in both groups

Fig. 4

Autoantibody isotype-related mean titer change of responders (RRs) and non-responders (NRRs) upon RTX -treatment. Mean titer course of IgM and especially IgA antibodies against MCV (AMCV) were significantly different in RRs and NRRs to RTX, with higher reductions in RRs after six months. Changes in RF isotypes and antibodies against CCP (ACCP) showed no significant difference between groups

Fig. 5

Individual IgA anti-MCV titer courses of responders and non-responders upon RTX treatment with mean titer change (red). Responders showed a greater tendency to reduce their initial titer from baseline to week 24 upon RTX treatment compared to non-responders, who rather remained stable

Fig. 6

Mean IgA anti-MCV titer course for responders and non-responders to RTX corresponding to their achieved Disease Activity Score 28 (DAS28) after RTX treatment. The achieved DAS28 and treatment response at week 24 according to the EULAR response criteria were reflected by the extent of anti-MCV IgA titer reductions. The better the DAS28 responses were, the greater the IgA anti-MCV reductions were. Responders in remission showed the greatest IgA anti-MCV reductions, whereas non-responders with high disease activity slightly increased their initial levels. EULAR, European League against Rheumatism; HDA, high disease activity; LDA, low disease activity; MDA, moderate disease activity

Fig. 7

Correlation of IgA anti-MCV and Disease Activity Score 28 (DAS28) in IgA anti-MCV-positive patients. The difference (delta) of anti-MCV IgA titers (delta anti-MCV IgA) from baseline to 24 weeks after RTX treatment correlated moderately with a greater improvement of DAS28 (delta DAS28) in anti-MCV IgA-positive patients (n = 21) (r = 0.49)

Fig. 8

Coincidence of autoantibody subtypes with anti-MCV (AMCV) IgA-positive and -negative patients at baseline. AMCV IgA-positive patients (purple) showed a greater overlap with RA-associated autoantibodies than AMCV IgA-negative patients (green), with significant coincidence of AMCV IgA, IgM and RF IgA