Abstract: FR-PO679

Immunodominant Epitope Regions and Clinical Outcome in THSD7A-Associated Membranous Nephropathy

Session Information

Category: Glomerular

  • 1001 Glomerular: Basic/Experimental Immunology and Inflammation

Authors

  • Seifert, Larissa, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Hoxha, Elion, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Eichhoff, Anna Marei, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Zahner, Gunther, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Koch-nolte, Friedrich, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Stahl, Rolf A., University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Tomas, Nicola M., University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Background

THSD7A has been identified as an autoantigen in patients with membranous nephropathy (MN). The epitopes targeted by patient autoantibodies are unknown.

Methods

In order to define the domain topology of THSD7A, we performed structure-based alignments with thrombospondin type 1 (TSP_1) domains in the protein data bank (pdb). We then cloned THSD7A fragments and tested for reactivity with serum from 31 patients with THSD7A-associated MN in a two-step approach using Western blotting. Clinical and serological follow-up was available from 16 of the 31 patients. We evaluated epitope profiles for associations with disease activity, incidence of malignancy, and clinical outcome.

Results

Protein structural analysis revealed a tandem string of 21 TSP_1 domains (d1 to d21). In a first unbiased approach, three consecutive fragments of the antigen (d1_d4, d5_d10 and d11_d21) were cloned, expressed in HEK293 cells, and tested for reactivity with patient autoantibodies. We found that 84% of patients recognized at least two of the constructs. Therefore, we cloned soluble fragments of 2-3 adjacent TSP_1 domains (d1_d2, d2_d3, d3_d4, d5_d6, d7_d8, d9_d10, d11_d12, d13_d14, d15_d16, d17_d18, d19_d21) in a second approach and tested again for serum reactivity. The d1_d2 fragment was recognized by 84% of the patients and therefore considered the immunodominant epitope region. However, epitope profiles among our patients varied greatly with 9 out of 11 TSP_1 domain fragments being recognized by at least three different sera. There was no association of epitope profiles with proteinuria, renal function or malignancy at the time of diagnosis. However, patients who recognized only one or two epitopes had lower anti-THSD7A antibody levels and less proteinuria. Among the patients with clinical and serological follow-up, 5 patients showed stable epitope profiles and persistent active disease, 8 patients lost reactivity with one or more constructs over time, and 3 patients showed a change in epitope profile during follow-up.

Conclusion

Our study demonstrates that autoantibodies in THSD7A-associated MN target a great variety of epitopes within the antigen. We could not identify epitope risk profiles regarding disease activity, clinical outcome during follow-up or incidence of malignancy.

Funding

  • Government Support - Non-U.S.