We undertook a sequential study in 29 children with steroid-sensitive nephrotic syndrome (SSNS) off treatment to seek evidence for T-cell activation in relapse. T-cell subsets and activation markers were analysed using two-colour flow cytometry. Soluble IL2 receptor (sIL2R) was measured in serum and urine by enzyme-linked immunosorbent assay (ELISA). Fifteen children were examined in remission and subsequent relapse (group A) and fourteen remained in remission (group B). In group A the proportion of CD4+ cells expressing the activation marker CD25 (alpha-chain of the IL2 receptor) increased significantly from remission to relapse: CD4+25+ cells rose from 5.6 to 7.0% of total lymphocytes, and from 15.8 to 19.1% of CD4+ lymphocytes (paired t test: P<0.0005 and <0.001 respectively). No correlations were found between CD4+25+ cells and plasma albumin or cholesterol concentrations. SIL2R concentration in serum did not change in relapse, but increased significantly in urine from 272 to 592 U/mg creatinine (P<0.01). No significant difference was found in remission between groups A and B. We conclude that early relapse in SSNS is associated with activation of CD4+ (T-helper) cells which is not secondary due to the nephrotic state itsel
