Detection and characterization of NELL1 autoantibodies in NELL1 positive membranous nephropathy

Abstract

Introduction: Discovery of novel autoantigens in membranous nephropathy provides promise for development of serologic tests to monitor disease activity and guide treatment. Neural epidermal growth factor-like 1 (NELL1) is the second leading antigen in membranous nephropathy, associated with malignancy, certain medications, and mercury poisoning. Anti-NELL1 antibodies are currently detected within patient sera by western blotting against NELL1 recombinant protein, but no high-throughput clinical assays are available.

Methods: Here, we detail the development of a quantitative ELISA and an indirect immunofluorescence assay for detection of anti-NELL1 antibodies within patient sera and demonstrate that circulating anti-NELL1 antibodies are predominantly IgG1 and IgG4.

Results: These assays had high specificity (94.9%-100%), but relatively low sensitivity (61.3%- 66.7%) compared to the reference standard, defined as biopsy-proven NELL1-positivity. ELISA demonstrated 83.9% overall agreement with the immunofluorescence assay and 82.8% with Western blot, compared to 72.4% overall agreement between the latter two assays.

Conclusions: Our study provides methods for serologic testing to be utilized for serologic evaluation of NELL1-associated membranous nephropathy. Further work will establish if antibody titters correlate with disease activity and response to immunosuppression.

Keywords: NELL1; enzyme-linked immunosorbent assay; indirect immunofluorescence assay; membranous nephropathy; serologic testing.