Membranous nephropathy is an immunologically mediated disease in which deposts of mainly IgG and complement collect in the basement membrane and appear in a diffuse granular pattern by immunofluorescence, as seen here. Membranous nephropathy can be secondary to an underlying malignancy, infection, drug ingestion, or SLE. It can be idiopathic. About 3/4 of persons with the idiopathic form have antibodies to phospholipase A2 receptor, a transmembrane cell surface receptor. Levels of this antibody can indicate the severity of disease.