Clinical Relevance of Domain-Specific Phospholipase A2 Receptor 1 Antibody Levels in Patients with Membranous Nephropathy
Authors: Reinhard Linda , Zahner Gunther , Menzel Stephan , Koch-Nolte Friedrich , Stahl Rolf A.K. , Hoxha Elion 
Published: December 2019

Significance Statement
Phospholipase A2 receptor 1 (PLA2R1) is the major target of autoimmunity in membranous nephropathy. Anti-PLA2R1 antibody levels predict treatment response and outcome in this disease. Earlier studies identified three target epitope regions in the PLA2R1 and proposed that having antibodies against more than one PLA2R1 epitope region had prognostic relevance. In this prospective study of a cohort of 150 patients with newly diagnosed membranous nephropathy, the authors identified a fourth epitope region targeted by anti-PLA2R1 antibodies. They also found that all sera recognized at least two distinct PLA2R1 domains at the time of diagnosis. Detection of domain-specific antibodies was highly dependent on total anti-PLA2R1 antibody levels. Anti-PLA2R1 antibody levels, but not PLA2R1 epitope-recognition patterns or domain-specific PLA2R1 antibody levels, predict treatment response and outcome (remission of proteinuria) in membranous nephropathy.

Background
Antibodies against phospholipase A2 receptor 1 (PLA2R1) are found in 80% of patients with membranous nephropathy, and previous studies described three autoantibody-targeted PLA2R1 epitope regions. Although anti-PLA2R1 antibody levels are closely associated with treatment response and disease prognosis, the clinical role of epitope regions targeted by autoantibodies is unclear.

Methods
In a prospective cohort of 150 patients with newly diagnosed PLA2R1-associated membranous nephropathy, we investigated the clinical role of epitope-recognition patterns and domain-specific PLA2R1 antibody levels by western blot and ELISA.

Results
We identified a fourth epitope region in the CTLD8 domain of PLA2R1, which was recognized by anti-PLA2R1 antibodies in 24 (16.0%) patients. In all study patients, anti-PLA2R1 antibodies bound both the N-terminal (CysR-FnII-CTLD1) region and the C-terminal (CTLD7-CTLD8) region of PLA2R1 at study enrollment. The total anti-PLA2R1 antibody levels of patients determined detection of domain-specific PLA2R1 antibodies, and thereby epitope-recognition patterns. A remission of proteinuria occurred in 133 (89%) patients and was not dependent on the domain-recognition profiles. A newly developed ELISA showed that domain-specific PLA2R1 antibody levels targeting CysR, CTLD1, and CTLD7 strongly correlate with the total anti-PLA2R1 antibody level (Spearman’s rho, 0.95, 0.64, and 0.40; P<0.001, P<0.001, and P=0.002, respectively) but do not predict disease outcome independently of total anti-PLA2R1 antibody levels.

Conclusions
All patients with PLA2R1-associated membranous nephropathy recognize at least two epitope regions in the N- and C-terminals of PLA2R1 at diagnosis, contradicting the hypothesis that PLA2R1 “epitope spreading” determines the prognosis of membranous nephropathy. Total anti-PLA2R1 antibody levels, but not the epitope-recognition profiles at the time of diagnosis, are relevant for the clinical outcome of patients with this disease.