Abstract: TH-OR027

Similarities between THSD7A and PLA2R Antigens in Autoimmune Membranous Nephropathy (AMN)

Session Information

Category: Glomerular

  • 1001 Glomerular: Basic/Experimental Immunology and Inflammation

Authors

  • Rhoden, Samuel, University of Manchester, Manchester, United Kingdom
  • Fresquet, Maryline, University of Manchester, Manchester, United Kingdom
  • Jowitt, Thomas A., University of Manchester, Manchester, United Kingdom
  • Gummadova, Jennet O., University of Manchester, Manchester, United Kingdom
  • Roberts, Ian, John Radcliff Hospital, Headington, Oxford, United Kingdom
  • Lennon, Rachel, University of Manchester, Manchester, United Kingdom
  • Brenchley, Paul E., Manchester Royal Infirmary, Manchester, United Kingdom
Background

Patients with AMN either have autoantibodies against PLA2R (75%) or THSD7A (2%). PLA2R and THSD7A proteins share similar structural and biochemical properties. Both proteins are large transmembrane receptors expressed on podocytes with multiple disulfide-bonded and N-glycosylated extracellular domains. We previously described the major epitope within PLA2R but the dominant epitope in THSD7A is still unknown.
Hypothesis: The major epitope in THSD7A may share shape homology with PLA2R.

Methods

Recombinant full length extracellular domains of THSD7A (FL 180kDa) and a fragment (NT 120kDa) were expressed, purified and used to screen 1400 AMN sera by ELISA for anti-THSD7A. Clinical phenotype on 10 cases was collected. Biopsies were stained for THSD7A and PLA2R. Sera were characterised by western blotting, ELISA and slot blotting on various THSD7A fragments and peptides. The homology model of the PLA2R CysR domain was used to thread the THSD7A epitope peptide.

Results

22 cases negative for anti-PLA2R were found anti-THSD7A positive (2%). We selected the 10 highest titre sera from the MN group (6F/4M mean age= 64yr). All 10 sera could be inhibited by the THSD7A NT fragment indicating an epitope(s) within this region. Interestingly a short sequence within the NT fragment shares homology with the PLA2R epitope. This short sequence peptide bound antibodies by slot blotting and inhibited binding to the antibodies by ELISA in all patients’ sera suggesting a potential epitope in THSD7A. Homology modelling of these two epitopes in PLA2R and THSD7A revealed two regions important for antibody binding.

Conclusion

We describe the first ELISA for anti-THSD7A and report an incidence of 2% positivity in a large cohort of anti-PLA2R negative AMN patients. We identified a specific region on THSD7A with structural homology to the major epitope in PLA2R and show this sequence to be a potential epitope in THSD7A. These results suggest a pathological epitope structure common to autoantigens involved in MN.

Funding

  • Private Foundation Support