Complement Receptor 1 Enhancement in Recurrent Membranous Nephropathy Following Kidney Transplantation: A Case Report.

Membranous nephropathy (MN) recurs in some kidney allograft patients, and recurrence increases graft failure rates. We present a unique case of recurrent MN in first and second allografts showing glomerular capillary wall-positivity for complement receptor 1 (CR1) consistent with immunoglobulin G (IgG). A man in his late 20s developed MN and started hemodialysis. MN recurred and caused graft loss after the first transplantation and recurred again soon after the second transplantation. The IgG subclass staining was almost consistently negative for IgG4 and phospholipase A2 receptor (PLA2R)-staining was negative. Recurrent MN of unknown etiology was considered. Mass spectrometry demonstrated that CR1 had increased in the transplanted kidney biopsies. Immunohistochemistry and immunofluorescence studies demonstrated CR1 colocalized with IgG along glomerular capillaries in this case, whereas CR1 was localized in podocytes with no colocalization of IgG in a control case of PLA2R-associated MN. Correlative light and immunoelectron microscopy showed localization of CR1 at the interface between electron-dense deposits and podocytes. Collectively, this case demonstrated a unique enhancement and localization of CR1. MN with enhancement of CR1 has not been reported to date. CR1 may be a candidate causative antigen in this case of recurrent MN, although further study is needed to investigate the pathogenesis of CR1.