Glomerular and serum IgG subclasses in diffuse proliferative lupus nephritis, membranous lupus nephritis, and idiopathic membranous nephropathy

Objective To determine whether a different renal histopathology is associated with the characteristic IgG subclass distribution, and whether a distinct IgG subclass distribution is involved in a unique immunopathological expression, we compared the distributions of glomerular and serum IgG subclasses in diffuse proliferative lupus nephritis (DPLN), membranous LN (MLN), and idiopathic membranous nephropathy (MN). Patients and Methods The glomerular IgG subclass distributions in patients with DPLN (n=7), MLN (n=10) or MN (n=16) were assessed by direct immunofluorescence microscopy. Serum levels of each IgG subclass were quantitated by ELISA in DPLN, MLN, and MN patients, and in normal human sera (NHS) (n=14). Results IgG1, IgG2, IgG3, and, to a lesser degree, IgG4 were similarly present in glomerular deposits in both DPLN and MLN. In contrast, IgG4 was the predominant glomerular IgG subclass in MN. Regarding the serum IgG subclasses, the mean IgG subclass concentrations and the mean proportion of each IgG subclass to the total IgG (%IgG subclass) in DPLN and MLN were not significantly different from those in NHS, except for the increased %IgG1 in MLN. In MN, the mean %IgG4 was selectively increased (p<0.01 vs NHS) in association with a slightly elevated IgG4 concentration; however, the mean concentrations of other IgG subclasses were significantly decreased (p<0.01 vs NHS), and the %IgG subclasses were not significantly different from those in NHS. Conclusions The results indicate that the IgG subclass distribution is not associated with the different renal histopathologies of DPLN and MLN. This study also shows the selective significance of IgG4 in MN, but not in MLN, another form of membranous glomerulopathy.