Phospholipase A2receptor-positive membranous nephropathy detected by laser microdissection and mass spectrometry in patients negative by immunofluorescence for phospholipase A2receptor on kidney biopsy.

Abstract

Introduction: Membranous Nephropathy (MN) is characterized by subepithelial deposition of immune complexes along the glomerular basement membrane. The muscle-type phospholipase A2 receptor (PLA2R) has been identified as the principal antigen in MN, and its detection via immunofluorescence (IF) studies remains a diagnostic cornerstone. Advancements, including Laser Microdissection/Mass Spectrometry (LMD/MS), offer enhanced sensitivity for antigen identification, independent of epitope accessibility.

Methods: A cohort of 250 kidney biopsy samples (discovery cohort) diagnosed as PLA2R-negative MN by IF underwent LMD/MS analysis for antigen detection. Biopsies were microdissected, and peptides were analyzed using high-performance liquid chromatography coupled with mass spectrometry. Total spectral counts greater than 10 are considered positive for PLA2R-associated MN.

Results: LMD/MS identified PLA2R antigen in seven (2.8%) cases classified as PLA2R-negative by IF. The mean total spectral count in the seven cases was 55. Additionally, LMD/MS detected another two positive cases in PLA2R-negative MN from a recently validated clinical test for antigen detection. The mean total spectral count in these two cases was 189. All nine cases showed significant IgG along the glomerular basement membrane. Electron microscopy showed stage II MN in seven of the nine cases, one case showed stage I, and the other showed stage III-IV MN. Serologic studies showed anti-PLA2R antibodies in two of seven cases with available data.

Conclusion: A small subset of PLA2R-negative MN by IF became PLA2R-positive by LMD/MS. Our study emphasizes the importance of not ruling out the possibility of PLA2R-associated MN in patients with negative IF staining for PLA2R. LMD/MS is an important diagnostic test for MN antigen detection.