Anti-vimentin antibodies: a unique antibody class associated with therapy-resistant lupus nephritis

Abstract

Background:: Tubulointerstitial inflammation (TII) in lupus nephritis (LN) is associated with a worse prognosis. Vimentin, a filamental antigen, is commonly targeted by in situ activated B-cells in TII. The prognostic importance of high serum anti-vimentin antibodies (AVAs) in LN and their relationship with common lupus autoantibody specificities is unknown. Herein we investigated associations between AVA isotypes, other autoantibodies, and response to mycophenolate mofetil (MMF) in the presence or absence of rituximab.

Methods:: The Translational Research Inititative in the Department of Medicine (TRIDOM) cross-sectional cohort of 99 lupus patients was assayed for IgG-, IgA- and IgM- AVAs, lupus associated and rheumatoid arthritis (RA) associated antibodies, and hierarchically clustered. Serum from baseline, 26 and 52 weeks from 132 LUNAR trial enrolled LN patients was also analysed and correlated with renal function up to week 78.

Results:: In TRIDOM, AVAs, especially IgM AVAs, clustered with IgG anti-dsDNA and away from anti-Sm and -RNP and RA associated antibodies. In LUNAR at baseline, AVAs correlated weakly with anti-dsDNA and more strongly with anti-cardiolipin titres. Regardless of treatment, IgG-, but not IgM- or IgA-, AVAs were higher at week 52 than at baseline. In contrast, anti-dsDNA titres declined, regardless of therapeutic regime. High IgG AVA titres at entry predicted less response to therapy.

Conclusion:: AVAs, especially IgG AVAs, are unique in distribution and response to therapy compared to other commonly measured autoantibody specificities. Furthermore, high-titre IgG AVAs identify LN patients resistant to conventional therapies. These data suggest that AVAs represent an independent class of prognostic autoantibodies.

Keywords: Vimentin; autoantibodies; lupus nephritis; prognosis; systemic lupus erythematosus.

Figure 1.

Clustered heat map of autoantibody titres in serum samples from the TRIDOM lupus cross-sectional cohort. Heat map cells represent individual patient serum sample titres, colored (see key below heat map) as percentages, relative to the maximum titre for the respective antibody specificity in the cohort. Titres of antibodies commonly assayed in the diagnosis of SLE (IgG anti-dsDNA, -RNP, -Sm) and RA (IgG anti-CCP, IgG RF, IgM RF and IgA RF) were compared to IgG, IgA and IgM isotypes of AVAs. A hierarchical cluster analysis was performed between the respective antibody specificities, using Ward’s minimum variance method and corresponding dendrogram displayed. Only patients for whom all indicated antibodies were titrated were included in the heat map. AVA=anti-vimentin antibody; CCP= cyclic citrullinated peptide 3; dsDNA=double-stranded DNA; RF=rheumatoid factor; RNP=ribonucleoprotein; Sm=Smith.

Figure 2.

Clustering of lupus associated autoantibody titres LUNAR baseline serum samples. Heat maps and dendrograms were plotted as for Figure 1, but for a larger cohort of lupus patients (and more extensive range of lupus associated autoantibodies) with class III and/or IV proliferative nephritis enrolled in the LUNAR trial. ACA=anti-cardiolipin; ANA=anti-nuclear antibody; 2GPI= 2 glycoprotein I; SSA=Sjögren’s syndrome antigen A, SSB=Sjögren’s syndrome antigen B; Vim_C-term=recombinant vimentin C-terminus (residues 260-466).

Figure 3.

Effect of different treatment regimens on titres of AVAs. (a) Relative (percentage) change in labelled isotypes of serum AVA from baseline in LUNAR patients. Medians and interquartile ranges (IQRs) from each group of patients’ titres are plotted for respective treatments. Mann Whitney tests were performed between serum titres in treatment groups for each time point. (b) Raw AVA titres at different time points for respective treatments (medians and IQRs are plotted, and Wilcoxon matched pairs signed rank tests performed between baseline and the indicated time points). Each dot represents an individual patient’s AVA titre. 0.01< *p <0.05, 0.01< **p <0.001, 0.001< ***p < 0.0001, ****p <0.0001, NS=non-significant.

Figure 4.

Disease activity changes (Δ) from baseline in LUNAR patients with high or low AVA titres. For each AVA subtype (sparated by row, labelled on the right hand side), all patients (both treatment regimens combined) were divided into AVA high (above median baseline AVA subtype titre) or AVA low (below median baseline AVA subtype titre) groups. ANOVA tests were performed between groups at each time point, and where significant indicated. 0.01<* p <0.05. UPCR=Urine protein/serum creatinine ratio; CREAT=serum creatinine; C3S=soluble complement factor C3. For each row, legends in the left most graph indicate the serological stratification of LUNAR patients.