Proteinuria and fusion of podocyte foot processes in rats after infusion of cytokine from patients with idiopathic minimal lesion nephrotic syndrome.

OBJECTIVE

We report on the isolation of a factor secreted by peripheral blood mononuclear cells from patients with idiopathic minimal lesion nephrotic syndrome (IMLNS) in relapse and its effect on proteinuria and podocyte morphology in the rat.

METHODS

Peripheral blood mononuclear cells from patients with IMLNS (in relapse and in remission) and patients with focal segmental glomerulosclerosis were cultured for 72 h. Supernatants from 20 x 10(6) cultured cells were separated by liquid chromatography into three fractions according to markers (bovine serum albumin, beta-amylase, and apoferritin). Each supernatant fraction was infused into rats for 5 days using an osmotic pump. Proteinuria, 24-hour albumin excretion or albumin/creatinine ratio in a 24-hour urine collection, was measured daily starting 3 days prior to fraction infusion. Renal tissue was obtained for electron microscopy studies. The beta-amylase fraction underwent electrophoresis using isoelectric focusing gel.

RESULTS

When protein excretion was compared prior to and during supernatant fraction infusion, a significant increase in proteinuria was observed only when beta-amylase fraction from IMLNS patients in relapse was infused (p < 0.05). Protein electrophoresis of the beta-amylase fraction showed a single band at pH 6.0 only in samples from IMLNS patients in relapse. The band was composed of two proteins, beta-amylase and a 100-kDa glycoprotein. Fusion of foot processes was observed only when the beta-amylase fraction from IMLNS patients in relapse was infused.

CONCLUSIONS

The infusion of the beta-amylase fraction containing a 100-kDa glycoprotein from IMLNS patients in relapse induced proteinuria and effacement of foot processes in the rat. This protein may play a role in the pathogenesis of IMLNS.