Serum IgG subclasses and IgM imbalances in adult IgA mesangial glomerulonephritis and idiopathic Henoch−Schoenlein purpura

Serum IgG subclass levels were investigated in 27 IgA GN and HSP patients and 19 healthy paired controls using a panel of monoclonal antibodies. IgG1 and IgG2 were statistically lower than in the controls in both the non-nephrotic and nephrotic patients, and 80% of the non-nephrotic patients exhibited a partial deficiency for either IgG1, IgG2 or IgG3. Urinary losses of IgG only accounted for decreased levels of IgG4. Fifty-four percent of these patients exhibited decreased IgM levels. This IgG-IgM imbalance may increase the susceptibility of these patients to viral and bacterial infections of the upper respiratory tract and trigger the renal disease. These findings raise the hypothesis that this IgG-IgM imbalance might be involved in the etiopathogenesis of these diseases.