IgG subclass composition of monomeric and polymeric IgG in the serum of patients with nephrotic syndrome

Abstract

The serum levels of immunoglobulins G, A and M and of the four subclasses of IgG have been measured in 54 patients with the nephrotic syndrome; 27 had minimal change disease (MCD), 9 membranous glomerulopathy (MGN), 5 focal glomerulosclerosis (FGS), 5 proliferative glomerulonephritis (PGN) and 8 miscellaneous forms of nephrotic syndrome (Table 1). Low levels of IgG and A, previously described in MCD, were found in all histological diagnoses; only about half the cases of MCD showed a high IgM. Measurement of the subclasses IgG 1-4 showed all to be depressed. Proportionately, however, the IgG2 was most affected (8.8% total IgG, cf 18.3% controls). Urinary protein loss, either total or IgG, only partially correlated with IgG suppression, while IgG2 in the urine usually comprised an even lower proportion of total IgG than in serum. The polyethylene glycol (PEG) 6,000 precipitate from serum at 4% concentration was also examined for IgG and subclasses in MCD (27 cases), MGN (9 cases) and PGN (3 cases). Raised levels above those of 14 normal controls were found in nearly all cases of MCD, even in remission, but in no cases of MGN. In MCD no IgG4 was found in any of the precipitates, while IgG2 was proportionately raised (22% of total) in the precipitate as compared with whole serum (8.8%). Serial studies on 9 adults (3 MCD, 3 MGN, 1 FGS, 1 PGN, 1 IgA nephropathy) showed only that the low levels of IgG and subclasses were associated with relapses and reverted toward normal in remission.