Soluble interleukin-2 receptor alfa predicts renal outcome in IgA nephropathy

Background. Both systemic and mucosal IgA production are controlled by T lymphocytes and infiltrating T lymphocytes are involved in the progression of interstitial fibrosis in chronic kidney disease (CKD). Since the concentration of soluble interleukin-2 receptor alfa (sIL-2Ra) reflects the degree of T cell activation over time, we studied the impact of interleukin-2 receptor alfa levels on disease progression in patients with biopsy-proven IgA nephropathy (IgAN), a disease in which 20-30% of the patients progress to end-stage renal failure. Methods. sIL-2Ra plasma levels were measured in 194 patients (median age 39 years, 70% men) and 84 matched controls. One hundred and seventy-nine of the patients, with an estimated glomerular filtration rate (GFR) of >= 15 mL/min/1.73m(2) at baseline (CKD Stages 1-4), were followed for up to 15 years (median 52 months; range 12-188). sIL-2Ra was evaluated as a risk marker for severe renal progression, here defined by the development of CKD Stage 5 (GFR <15 mL/min/1.73m(2)), a 50% decline in GFR during the follow-up period or a 30% GFR decline within 5 years of follow-up. In 51 patients, upon whom a renal biopsy had been performed within 2 years of IL2-Ra measurement, the biopsies were scored according to the Oxford classification. The correlations between the histopathological findings and the sIL-2Ra levels were examined. Results. sIL2-Ra levels were significantly higher in patients than in controls (P < 0.001). sIL-2Ra levels in the upper third tertile predicted a severe renal outcome, even after adjustment for the main clinical risk factors: time average albuminuria and GFR at baseline (Relative risk 5.35, P < 0.001). sIL-2Ra levels also correlated significantly to the yearly GFR slope (beta = -0.24, P = 0.01). According to the Oxford classification, the presence of >25% tubular atrophy/interstitial fibrosis (T1-2) was associated with higher sIL-2Ra levels, after adjustment for serum creatinine levels, if analysed within 4 months [n = 24, odds ratio (OR) 1.0, P = 0.044] or within 2 years from the kidney biopsy (n = 51, OR 1.0, P = 0.017). Conclusions. The plasma levels of sIL-2Ra were predictive of long-term renal disease progression in a large cohort of patients with biopsy-proven IgAN. Further studies are warranted to evaluate if sIL-2Ra levels can feasibly contribute in the monitoring of effects of treatment, aimed to prevent the progression of interstitial fibrosis and progressive glomerulosclerosis in IgAN.