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Abstract: PO1474

Positive PLA2R Detection by Mass Spectrometry but Negative PLA2R Staining on Immunofluorescence Microscopy

Session Information

Category: Glomerular Diseases

  • 1202 Glomerular Diseases: Immunology and Inflammation

Authors

  • Sethi, Sanjeev, Mayo Clinic Minnesota, Rochester, Minnesota, United States
  • Madden, Benjamin J., Mayo Clinic Minnesota, Rochester, Minnesota, United States
  • Zand, Ladan, Mayo Clinic Minnesota, Rochester, Minnesota, United States
  • Fervenza, Fernando C., Mayo Clinic Minnesota, Rochester, Minnesota, United States
Background

Detection of PLA2R along the glomerular basement membranes by immunofluorescence (IF) studies using antibodies directed against PLA2R is considered the gold standard for diagnosis of PLA2R-positive MN on the kidney biopsy. Laser microdissection of glomeruli followed by mass spectrometry (MS) of PLA2R-positive MN also detects high total spectral counts of PLA2R confirming the IF studies. However, correlation of PLA2R-negative MN cases by both IF and MS has not been done.

Methods

We performed laser microdissection and mass spectrometry in 230 cases PLA2R-negative MN in search of novel proteins that may represent new target antigens in PLA2R-negative MN. All 230 cases were negative for PLA2R by IF staining.

Results

We detected high total spectral counts of PLA2R in 8 (3.5%) of the 230 PLA2R-negative MN cases by IF. The mean total spectral count of PLA2R in the 8 cases was 57 (range 24 to 83, SD ± 25.0) (Figure 1). This is comparable to the mean total spectral counts in PLA2R-positive MN (57.7 ± 23.7). The baseline mean total spectral count of PLA2R in 6 time zero transplant biopsies (control cases) was 6. Interestingly, all subtypes of IgG were present in the 8 cases that were postivie for PLA2R by MS with IgG1 being the dominant (total spectral count 57 ± 16.9) followed by IgG3 (50.0 ± 11.5), IgG4 (46.3 ± 18.1) and IgG2 (39.3 ± 11.4). On kidney biopsy, 3 of the 8 cases showed findings for secondary autoimmune MN such as C1q positivity or full house Ig staining. Electron microscopy showed stage I MN in 2 cases, stage II MN in 5 cases and stage III in 1 case. Clinical details at presentation were as follows: 3 females and 5 males, mean age 53.6 years (± 20.7), mean serum creatinine 1.38 mg/dL (± 0.6), and mean proteinuria 6.8 gms/24 hours (± 6.2).

Conclusion

IF is negative for PLA2R-staining in a small (3.5%) number of PLA2R-postive MN. These cases can be detected by MS. Thus, MS is an alternative to IF staining and the new gold standard to detect PLA2R on the kidney biopsy.

MS studies showing high total spectral counts of PLA2R in 8 cases that were PLA2R-negative by IF. Baseline mean levels of PLA2R in 6 controls (Ctrls) are shown in first column.