Background/Purpose: Severe lupus tubulointerstitial nephritis (TIN) is prognostic of renal failure and characterized by an in situ autoantibody response. By characterizing monoclonal antibodies engineered from in situ activated B cells and plasmablasts using mass spectrometry and whole protein arrays we identified vimentin as the dominant antigen targeted by this in situ immune response. Direct binding of mAbs and TIN serum IgG to vimentin, together with multi-color confocal microscopy of lupus kidney samples confirmed autoantibody reactivity and that vimentin was a dominant autoantigen expressed in the inflamed tubulointerstitium. To understand the origin and evolution of this anti-vimentin antibody response we mapped the specific epitopes these antibodies recognized and, by reversion to germline, identified their original antigenic specificities.

Methods: Twelve IgG1 mAbs previously cloned from the inflamed tubulointerstitium of 6 lupus patients were expressed. Those with the highest anti-vimentin immunoreactivity were reverted to germ-line. Selected antibodies were then screened for immunoreactivity against purified bovine vimentin, recombinant human vimentin expressed in bacteria and vimentin that had been citrullinated (and confirmed as such by mass spectrometry) by PAD4. Nimblegen peptide arrays covering the entire human proteome as overlapping 12mers were probed.

Results: Previously characterized anti-vimentin antibodies bound directly to recombinant human vimentin and this binding was strongly inhibited by in vitro citrullination.  Immunoreactivity with recombinant human vimentin and purified bovine vimentin was similar suggesting that no post-translational modifications were required for antibody binding. Using the Nimblegen arrays, we identified two epitopes within vimentin that both contained arginines and which were potential sites of citrullination. When anti-vimentin antibodies were reverted to germline, they still recognized vimentin but with a relative affinity significantly less than the mutated parent antibody.

Conclusion: These data indicate that the in situ humoral immune response in lupus tubulointerstitial nephritis is specific for vimentin that has not been citrullinated and therefore is fundamentally different than that associated with rheumatoid arthritis.  Furthermore, this immune response arises from a naïve repertoire already reactive with vimentin and not with the nuclear antigens most often associated with systemic lupus erythematosus.  These data suggest that unique mechanisms of in situ antibody selection drive local inflammation in lupus tubulointerstitial disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-resolution-motif-mapping-of-ae%cb%9cin-situae-anti-native-vimentin-antibodies-in-lupus-tubulointerstitial-nephritis/