OBJECTIVETo study serum concentration and mRNA expression of interleukin-13 (IL-13) in children with steroid-responsive nephrotic syndrome (SRNS) and the effect of methylprednisolone pulse therapy (MPT) on IL-13 expression.

METHODSTwenty-eight children with SRNS were enrolled in this study. Serum protein level of IL-13 was measured using ELISA and IL-13 mRNA expression in peripheral blood mononuclear cells (PBMC) was detected with RT-PCR before MPT, 2 and 5 days after MPT, and 2 weeks after disappearance of proteinuria following MPT. Twenty-four urinary protein was measured with the biuret assay. Twenty healthy children were used as controls.

RESULTSSerum IL-13 levels (38.48 +/- 13.01 pg/mL vs 5.18 +/- 2.71 pg/mL) and PBMC IL-13 mRNA expression (1.31 +/- 0.23 vs 0.36 +/- 0.07) before MPT in SRNS patients were significantly higher than in the controls. After 5 days of MPT and 2 weeks after disappearance of proteinuria following MPT, serum IL-13 levels (15.33 +/- 7.81 and 5.35 +/- 2.12 pg/mL respectively) and PBMC IL-13 mRNA expression (0.89 +/- 0.26 and 0.33 +/- 0.08 respectively) were significantly reduced (P < 0.01). Serum IL-13 levels and PBMC IL-13 mRNA expression in SRNS patients 2 weeks after disappearance of proteinuria following MPT were reduced to control levels, but remained at a higher level than controls 5 days after MPT. A positive correlation was found between serum levels of IL-13 and 24-hour urinary protein in SRNS patients before (r=0.75, P < 0.01) and after 2 and 5 days of MPT (r=0.68, r=0.71 respectively; P < 0.05).

CONCLUSIONSSerum IL-13 levels and PBMC IL-13 mRNA expression in children with SRNS increase. MPT can inhibit the expression of protein and mRNA of IL-13 in these patients.