Detection and characterization of NELL1 autoantibodies in NELL1 positive membranous nephropathy.

Abstract

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. 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. 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. 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.