Immunoglobulin sysnthesis and urinary IgG excretion in the idiopathic nephrotic syndrome of children

Biochemical and clinical findings suggest that children with lipoid nephrosis (INS) and x-linked immunodeficiency with normal to elevated IgM (Dys-M) may represent a similar underlying pathologic process. To evaluate this possibility we compared in vitro immunoglobulin production by blood lymphocytes from 10 children with INS, 2 children with Dys-M, II uninfected children of similar age and simultaneously cultured adult controls. Children with INS showed decreased serum levels of IgG (>2 SD below the mean for age-matched controls) and normal levels of IgM and IgA. Patients with Dys-M demonstrated characteristic low levels of IgG and IgA, and normal to elevated IgM. Lymphocytes from children with Dys-M did not produce detectable amounts of immunoglobulins. In contrast, lymphocytes from all children with or without INS and adult controls showed significant stimulation of immunoglobulin production by pokeweed mitogen. Thus the hypogammaglobulinemia in INS and Dys-M does not appear to have a similar etiology. To evaluate another cause of decreased serum IgG concentration in patients with INS, we measured urinary IgG in 9 of the children. IgG excretion ranged from 0.15 to 37.8 mg/24 hrs (mean, 18.0 ± 5.3). This represented from <1 to 7.3% of the total protein excreted. There was no significant correlation between serum IgG and urinary excretion of IgG (r= -.334, p > > .1). Thus the urinary loss of IgG is not sufficient to explain the observed hypogammaglobulinemia. Other explanations for the lower serum IgG might include a humoral factor that decreases IgG production in vivo or other factors which may cause increased catabolism of IgG.