Background/Purpose: Patients with ANCA vasculitis and anti-glomerular basement membrane (GBM) nephritis (Goodpasture’s Disease) develop pathogenic autoantibodies (autoAb) that destroy the microvasculature in lungs and kidneys. A substantial subset of patients develops double-positive (DP) ANCA+ anti-GBM+ autoAb and a clinical overlap syndrome. A recent analysis of a large patient cohort suggests that clinical relapse is particularly likely in the surviving DP patients with anti-PR3 ANCA. Little is known about the sequence and structure of autoAb of either specificity or about the relationship between ANCA and anti-GBM autoAb in DP patients. To gain insight into the origins of human anti-PR3 DP autoAb, we took advantage of the HuHSC-NSG model in which conditioned immunodeficient NOD-scid-gamma (NSG) mice are injected with human hematopoietic stem cells (HSC) to reconstitute a human immune system in vivo.

Methods: We measured binding to purified native human PR3 in two panels of HuHSC-NSG-derived human antibodies: 1) Six clonally unrelated human anti-GBM monoclonal antibodies (mAb) previously generated from collagen-immunized HuHSC-NSG mice and selected for binding to the non-collagenous domain-1 of the alpha3 chain of collagen IV, the antigen targeted by pathogenic anti-GBM autoAb; and, 2) Serum from a cohort of HuHSC-NSG mice (n=29) 4-6 months post engraftment and 1-3 months post aspiration of vehicle (saline) or crystalline silica, the environmental exposure most compellingly linked to human autoimmunity including ANCA vasculitis. Results using ELISA are reported as mean sample OD after subtraction of mean OD on diluent-coated plates.

Results: Two human anti-GBM mAb bound to PR3 (ODs = 0.618 and 0.455; positive control ANCA+ patients’ plasma IgG diluted 1:50 mean OD = 1.376). PR3 binding did not reflect broad polyreactivity, as neither mAb bound to MPO or Hep-2 cells. Low level anti-PR3 activity (mean OD = 0.084, diluted 1:50) was detected among human antibodies in the blood of a subset of silica-exposed HuHSC-NSG subjects derived from the same HSC unit.

Conclusion: Detection of both anti-GBM and anti-PR3 specificities in individual human mAb confirms that a single immunoglobulin can bind both autoantigens and that anti-GBM and anti-PR3 autoAb can share genetic origins. Prior sequence analysis of the human mAb revealed uncommon motifs that favor autoreactivity and are typically selected against in the immune repertoire. Our findings in humanized immune system mice suggest that genetics of the HSC donor and permissive environmental exposures may facilitate their expression. Sequence analysis of single-positive anti-PR3 and patients’ pathogenic autoAb will provide further insight into their genetic relationship and immune regulation, as well as potential novel targets for therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/shared-genetic-origins-among-anti-proteinase-3-and-anti-glomerular-basement-membrane-double-positive-human-autoantibodies/