Kidney Week

Abstract: FR-PO958

Phospholipase A2 Receptor (PLA2R)-Positive Membranous Nephropathy by Laser Microdissection and Mass Spectrometry in Patients with Negative Routine Immunofluorescence Microscopy for PLA2R on Kidney Biopsy

Session Information

• Pathology and Lab Medicine - 1
  October 25, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Pathology and Lab Medicine

• 1800 Pathology and Lab Medicine

Authors

• Russo, Ilario, Mayo Clinic Division of Nephrology and Hypertension, Rochester, United States

Ilario Russo, MD

• Zand, Ladan, Mayo Clinic Division of Nephrology and Hypertension, Rochester, Minnesota, United States

Ladan Zand, MD

• Fervenza, Fernando C., Mayo Clinic Division of Nephrology and Hypertension, Rochester, Minnesota, United States

Fernando C. Fervenza, MD, PhD, FASN

• Madden, Benjamin J., Mayo Clinic Minnesota, Rochester, Minnesota, United States

Benjamin J. Madden

• Sethi, Sanjeev, Mayo Clinic Department of Laboratory Medicine and Pathology, Rochester, Minnesota, United States

Sanjeev Sethi, MD, PhD

Background

The discovery of novel antigens in membranous nephropathy (MN) was done using laser microdissection followed by mass spectrometry (LMD/MS). Direct immunofluorescence microscopy (IF) for PLA2R was used to classify MN into PLA2R-positive MN and PLA2R-negative MN. PLA2R-negative MN cases were then used to detect novel antigens.

Methods

250 cases of PLA2R-negative MN were studied in the discovery cohort. All 250 cases had bright granular staining for IgG and were negative for PLA2R along the glomerular basement membrane by IF. The glomeruli were microdissected and the peptides were separated with a high-performance liquid chromatography (HPLC) system coupled to a Mass Spectrometer. Protein quantification was obtained via spectral counting.

Results

10 out of 250 (4%) patients with negative IF studies for PLA2R were positive for PLA2R on LMD/MS. Baseline PLA2R counts are typically in the range of 0-5 in PLA2R negative cases. The total spectral count (TSC) in the PLA2R positive by LMD/MS ranged from 13 to 75 (avg 39.5, ± 20.56) in the 10 cases. Only 3 cases showed moderate TSC of 13, 15 and 18, whereas the remaining cases shows high TSC ranging from 28 to 75. Of the available data in 7 patients, 2 had positive serum anti-PLA2R antibodies. The baseline clinical and demographic characteristics are shown in Table 1.

Conclusion

LMD/MS is a new methodology to detect the antigens in MN. 4% of PLA2R-negative MN by IF were positive for PLA2R by LMD/MS. LMD/MS appears to be more sensitive in detecting PLA2R than conventional IF.

Table 1.