*2.1. Kidney Analyses*

Kidney biopsies were performed under ultrasound guidance by an experienced investigator. Paraffin-embedded sections were routinely stained with periodic acid Schiff and assessed by light microscopy. Fluorescence staining for IgG, IgA, immunoglobulin M (IgM), C3c and C1q was performed on freshly frozen renal tissues and ultra-thin sections stained with uranyl acetate and lead nitrate were examined by electron microscopy as described in [16]. Kidney biopsies were frozen in isopentane chilled with liquid nitrogen. Six-micrometer thick cryostat frozen sections were performed for enzyme histochemical staining for Complex IV (COX), Complex II (SDH) and nicotinamide adenine dinucleotide (NADH) dehydrogenase activities using specific substrates of these enzymes including Cytochrome *c* (C7752, Sigma-Aldrich), β-nicotinamide adenine dinucleotide (N7410, Sigma-Aldrich, St. Louis, MO, USA) and succinic acid (S3674, Sigma-Aldrich), respectively as described [27–29]. Optical density

quantification of these activities was assessed from 20 consecutive microscopic fields in each renal section and the adjacent background regions.
