OBJECTIVES: T cells play an important role in the pathogenesis of lupus nephritis (LN). We studied the role of urinary soluble CD25 (sCD25) as a biomarker of LN disease activity in a cross-sectional and longitudinal study.
METHODS: Patients with systemic lupus erythematosus were classified as active LN (AN), inactive disease (ID) and active non-renal (ANR) based on disease activity and renal involvement at the time of enrolment. Urine and serum samples were collected at baseline from all patients and at 3-monthly follow-up from patients with AN. SLE disease activity index (SLEDAI) was used for disease activity assessment at all visits. sCD25 was measured by ELISA and normalized to urinary creatinine excretion and is expressed as pg/mg. Urine samples from 10 healthy individuals (HC) served as controls.
RESULTS: There were 119 patients (111 females, median age 27 years, 57 AN, 43 ID, 19 ANR). Median SLEDAI was 18, 2 and 8 in AN, ID and ANR groups, respectively. Median renal SLEDAI in AN was 8. Mean (±SD) urinary sCD25 in the AN, ID, ANR and HC groups at baseline was 741.1 (±794.9), 407.8 (±511.1), 735.4 (±667.7) and 250.9 (±122.2) pg/mg respectively (p = 0.019). Mean (±SD) serum sCD25 in AN, ID and ANR was 8285.25 (±5922.2), 6044 (±3501.92) and 6568.72 (±4333.62) pg/ml, respectively. Urinary sCD25 correlated with SLEDAI (r = 0.22; p = 0.015) but did not correlate with serum sCD25 or proteinuria. Urinary sCD25 compares well with traditional markers of disease activity in differentiating active from inactive renal disease. On follow-up mean urinary sCD25 decreased to 470.0 (±449.6; p < 0.05) at 3 months, 496.7 (±465.8; p = 0.006) at 6 months, 471.9 (±303.2; p = 0.041) at 9 months and 358.6 (±496.9; p = 0.007) at 12 months from baseline value of 741.1 (±794.9). In four patients who either had relapse, persistent disease activity or developed chronic kidney disease, urinary sCD25 showed rise preceding traditional abnormalities on urine examination.
CONCLUSIONS: Urinary sCD25 is a good biomarker for follow-up of LN. It may also have the potential to predict poor response and relapse.
