Elevated serum IL-21 levels in hantavirus-infected patients correlate with the severity of the disease.

Hemorrhagic fever with renal syndrome (HFRS) is an acute viral infection caused by Hantavirus (HTV). Capillary leakage is one of the hallmarks of HTV infection. The mechanisms underlying the pathogenesis of HFRS are not completely understood. However, it has been suggested that immune mechanisms, including cytokines, might have an important role in HFRS pathogenesis. In this study, we investigated the potential role of interleukin-21 (IL-21) which is a newly discovered cytokine that stimulates T-cell and B-cell responses in the pathogenesis of HFRS. Serum samples were collected from 58 patients hospitalized with laboratory-verified HTV infection and 20 healthy controls. Serum IL-21 concentration was measured using an enzyme-linked immunosorbent assay. Serum IL-21 levels began to increase in the fever phase when renal damage appeared. The highest serum IL-21 level was detected in oliguric phase along with the peak degree of urinary renal impairment. When entering the polyuric phase, with gradual increase in urine and recovered renal function, the serum IL-21 level was observed to fall, returning to normal level after the renal function recovered in the convalescent phase. The serum IL-21 level was positively correlated with blood urea nitrogen (BUN) and creatinine (Cr), suggesting that the serum IL-21 level is associated with the disease severity of HFRS. This study indicated that IL-21 may act as an important inflammatory mediator in the immunopathogenesis of HFRS. The strategy to control IL-21 may hamper the immune response in patients with HFRS.