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Abstract: SA-PO337

Proteomic Analysis of Complement Factors in PLA2R-Positive Membranous Nephropathy

Session Information

Category: Glomerular Diseases

  • 1202 Glomerular Diseases: Immunology and Inflammation

Authors

  • Sethi, Sanjeev, Mayo Clinic, Rochester, Minnesota, United States
  • Madden, Benjamin J., Mayo Clinic, Rochester, Minnesota, United States
  • Charlesworth, Cristine, Mayo Clinic, Rochester, Minnesota, United States
  • Cattran, Daniel C., Toronto General Hospital, Toronto, Ontario, Canada
  • Fervenza, Fernando C., Mayo Clinic, Rochester, Minnesota, United States
Background

Membranous nephropathy (MN) is characterized by deposition of immune-complexes and complement factors along the glomerular basement membrane. Phospholipase A2 receptor (PLA2R) is the target antigen in approximately 70% of MN. Although complement deposition is seen PLA2R-associated MN, a comprehensive and detailed analysis of complement factors in PLA2R-associated MN has not been done.

Methods

We used laser microdissection and mass spectrometry (MS) to dissect glomeruli and identify the glomerular and complement proteins in 7 cases of PLA2R-associated MN. For control cases, we used 6 cases of time 0 transplant protocol biopsies.

Results

MS identified very high total spectral counts (TSC) for PLA2R in all cases of PLA2R-associated MN with average TSC of 87 (range 45-135). In comparison, the avarage TSC in control cases was only 5 (range 0-7) which is similar to many house-keeping proteins. With regards to complement factors, C3 was the most abundant complement protein with average TSC of 413 (range 324-708), followed by C4 (C4-B avg 176, C4-A avg 174). Moderately high TSC of C9 (avg 79,) and C5 (avg 54) were also detected. Lesser amounts of C6 (avg 31) , C7 (avg 20) and C8 (avg 21) were also present. C1 was absent or present in very low spectral counts. In addition, complement regulating facors- complement factor H (avg 57), complement factor H-related protein 5 (avg 65.5) and complement factor H-related protein 1 (avg 30) were also detected.The average TSC of complement factors in control cases for C3, C4-B, C4-A and C5 was 107, 40, 39, and 5, respectively. With regards to immunoglobulins (Ig) in PLA2R-associated MN, IgG4 was the most abundant Ig (avg 91), followed by IgG1 (avg 68), IgG3 (avg 64) and IgG2 (avg 49). The avgerage Ig total TSC in control cases for IgG4, IgG1, IgG3 and IgG2 was 22, 56, 45 and 45, respectively.

Conclusion

Using MS analysis, we show accumulation of large amounts of C3 and C4, followed by C9 and C5, and lesser amounts of C6, C7 and C8 indicating a role of complement in the pathogenesis of PLA2R-associated MN. The TSC of C3 and C4 was much higher than the TSC of PLA2R or Ig indicating amplification and accumulation of complement factors in greater amounts than the PLA2R antigen or Ig. The large amounts of C3 and C4 and absence of C1 suggests involvement of the lectin pathway.