IgG purification
IgG was purified from plasma of patients with LN or of healthy donors, by using Protein G beads (GE Healthcare), as recommended by the manufacturer. The concentration of the IgG was determined by a Nanodrop and the purity of IgG – by 10% SDS-PAGE electrophoresis (Invitrogen, Life technologies, Novex), followed by a Coomassie Blue staining of the gel.