Immunological Interaction of HLA-DPB1 and Proteinase 3 in ANCA Vasculitis is Associated with Clinical Disease Activity

Abstract

Background: PR3-ANCA vasculitis has a genetic association with HLA-DPB1. We explored immunologic and clinical features related to the interaction of HLA-DPB1*04:01 with a strongly binding PR3 peptide epitope (PR3225-239). Methods: ANCA vasculitis patients with active disease and in remission were followed longitudinally. Peripheral blood mononuclear cells from patients and healthy controls with HLA-DPB1*04:01 were tested for HLA-DPB1*04:01 expression and interaction with a PR3 peptide identified via in silico and in vitro assays. Tetramers (HLA/peptide multimers) identified autoreactive T cells. Results: HLA-DPB1*04:01 genotype was associated with risk of relapse in PR3-ANCA (HR for relapse 2.06 (1.01, 4.20)) but not in the myeloperoxidase (MPO)-ANCA or the combined cohort. In silico predictions of HLA and PR3 peptide interactions demonstrated strong affinity between ATRLFPDFFTRVALY (PR3225-239) and HLADPB1*04:01 that was confirmed by in vitro competitive binding studies. The interaction was tested in ex vivo flow cytometry studies of labeled peptide and HLA-DPB1*04:01-expressing cells. We demonstrated PR3225-239 specific autoreactive T cells using synthetic HLA multimers (tetramers). Patients in long-term remission off therapy had autoantigenic peptide and HLA interaction comparable to that of healthy volunteers. Conclusion: The risk allele HLA-DPB1*04:01 has been associated with PR3-ANCA, but its immunopathologic role was unclear. These studies demonstrate that HLA-DPB1*04:01 and PR3225-239 initiate an immune response. Autoreactive T cells specifically recognized PR3225-239 presented by HLA DPB1*04:01. While larger studied should validate these findings,, the pathobiology may explain the observed increased risk of relapse in our cohort. Moreover, lack of HLA and autoantigen interaction observed during long-term remission signals immunological non-responsiveness.

PRTN3 variant correlates with increased autoantigen levels and relapse risk in PR3-ANCA versus MPO-ANCA disease

“…Additionally, our results underscore that disease phenotype in ANCA vasculitis may be contingent on autoantigen availability resulting from dysregulated autoantigen gene expression. We have previously shown that an epitope-specific response drives T cell response in MPO- and PR3-ANCA ( 14 , 15 ). Increased presence of pathogenic autoantigen epitopes may further impact the adaptive response.…”

“…Risk of relapse within the PR3-ANCA cohort was not based on variant carrier status. Possible explanations include other clinical differences in patients with PR3-ANCA or other genetic influences, such as HLA variants, that predispose patients with PR3-ANCA to likelihood of relapse ( 15 ).…”

Identifying Antigen-Specific T Cells in ANCA-Associated Vasculitis: A Glimpse of the Future?

“…1 Volume-regulated anion currents (VRACs) were first described in 1988, 2 and their electrophysiologic properties have been examined in a variety of cell types. 3,4 However, the molecular identity of VRACs remained enigmatic for a long time until the leucine-rich repeat-containing 8 member A channel (LRRC8A; also known as SWELL1) was identified in 2014. 5,6 LRRC8A can itself form functional hexamers, or it may assemble in herteromers with other members, including LRRC8B, LRRC8C, LRRC8D, and LRRC8E, to produce anion-conducting channels with unique biophysical properties.…”

“…The re-emergence of measurable B cell autoimmunity, in the form of PR3-ANCA, increases the risk of relapse, but ANCA cannot be used alone to dictate therapy. Assessing both T and B cell autoimmunity with other markers of inflammation, may allow for better definition of immunologic remission and improved assessment of the risk and detection of relapse 3 . In this issue of JASN Chen et al 3 begin to address this issue by examining PR3-specific CD4+ T cells in PR3-AAV.…”

“…Assessing both T and B cell autoimmunity with other markers of inflammation, may allow for better definition of immunologic remission and improved assessment of the risk and detection of relapse 3 . In this issue of JASN Chen et al 3 begin to address this issue by examining PR3-specific CD4+ T cells in PR3-AAV.…”