NELL-1–ASSOCIATED MEMBRANOUS NEPHROPATHY IN A NORTH INDIAN COHORT

Neural epidermal growth factor-like 1 (NELL-1) has recently emerged as a novel target antigen in primary and secondary membranous nephropathy (MN), linked to malignancies, autoimmune diseases, heavy metals such as mercury, and thiol-containing drugs. Mercury exposure through traditional medicines is a notable pathogenic trigger, particularly in South India. However, regional data from North India remain scarce. This study aimed to identify and characterize NELL-1 in PLA2R/THSD7A double-negative MN using integrated clinical, histopathological, serological, and proteomic profiling, while exploring mercury exposure as a potential etiological factor and establishing a Dynabead-based immunoprecipitation LC–MS workflow for multiplex antigen discovery.

An ambispective cohort of MN cases (2021–2025) was analyzed at a tertiary care center. Renal biopsies were screened using routine histopathology methods – Light Microscopy (LM), Electron Microscopy (EM), and Direct/Paraffin Immunofluorescence (IF). PLA2R and THSD7A were evaluated using our established immunostaining protocols, followed by standardized NELL-1 IF. Circulating NELL-1 autoantibodies were detected by Western blot using recombinant antigen, patient sera, and goat anti-human IgG, visualized via ECL (Bio-Rad/Thermo Fisher). Blood and urine mercury and other heavy metals were quantified using ICP–MS to assess etiological factors. To address the growing spectrum of MN antigens, a Dynabead-based immunoprecipitation–LC–MS workflow was optimized for antigen discovery in antigen-negative cases. All findings were correlated with clinical parameters, secondary associations (autoimmune diseases, toxic exposures, malignancies, viral markers), treatment regimens, and outcomes, including remission status, proteinuria, and serum albumin levels.

In our primary MN cohort, 34% of PLA2R/THSD7A-negative cases were NELL-1–positive, corresponding to 16% of all primary MN cases, with 55.5% confirmed by Western blot (follow-up showed reduced bands post-immunosuppression). NELL-1 patients had a 1:1 male-to-female ratio, a mean age 39 years, 25.8% reporting CAM intake (mean 11 months), and 9.7% using skin-brightening creams, of whom 7.7% showed very high mercury levels. Three dual-positive cases (PLA2R+/NELL-1+) also highlighted antigenic heterogeneity. G-Dynabead IP LC–MS/MS revealed high-intensity PLA2R spectra with broad peptide coverage and strong IgG4 control, and the workflow is now being applied to NELL-1. We also report the second global and first Indian pediatric NELL-1–positive MN in Wilson’s disease post-penicillamine, achieving remission with drug withdrawal and ACE inhibition, linking thiol drugs to antigen-driven podocytopathy. 

NELL-1–associated MN is highly prevalent among PLA2R/THSD7A-negative North Indian patients. Although mercury-associated MN is limited compared to studies from South India, identifying etiological factors remains crucial, as withdrawal or treatment of the underlying cause can lead to remission. Moreover, G-Dynabead IP LC–MS/MS is a promising approach that enables robust multiplex antigen profiling and could be a game-changer. Long-term follow-up and patient education are also essential. The study highlights the need for tailored, antigen-based classification and patient-specific management.

Some data in this abstract were previously presented at ISRTPCON 2024 and MPAICON 2025.; however, this version includes additional findings and modifications. Resubmission is allowed by the original meeting organizers.