Elevated plasma interleukin 21 is associated with higher probability and severity of idiopathic membranous nephropathy

Abstract Objectives Interleukin 21 (IL-21) is a receptor participating in innate immunity and correlates with the activation of innate immune cells. We sought to investigate the role of plasma IL-21 in patients with idiopathic membranous nephropathy (IMN). Methods This was a cross-sectional and case-control study. We analyzed plasma IL-21 in patients with IMN, with other kidney diseases as the diseased controls (DCs), and the healthy controls (HCs), regarding their associations with the risk of having IMN and IMN severity. Results We enrolled 132, 22, and 38 patients with IMN, DC, and HC, respectively. Plasma IL-21 was significantly higher in those with IMN [9.42 (6.93, 12.60)] and DC [7.84 (2.90, 7.95)] compared with HC [5.60 (2.90, 7.10)] (p<0.05). Plasma IL-21 was significantly higher in those with IMN stage III [10.36 (6.94, 20.88)] and II [9.75 (7.60, 14.27)] than those with IMN stage I [6.99 (3.91, 9.08)] (p<0.05). Plasma IL-21 was significantly higher in those with a positive anti-phospholipase A2 receptor antibody (PLA2R) [9.60 (8.27, 12.93)] than those with a negative anti-PLA2R antibody [4.84 (2.90, 11.28)] (p<0.05). Receiver operator characteristic curve analysis showed that a cutoff value of 7.665 pg/mL distinguished patients with IMN from HC and DC with a sensitivity and specificity of 68.94 and 89.47 %, respectively, and the area under the curve was 0.8184. A cutoff value of 7.830 pg/mL identified those with IMN stage II with a sensitivity and specificity of 74.03 and 89.47 %, respectively, with an area under the curve of 0.8718 (p<0.001). Multivariate regression showed that plasma IL-21 was positively correlated with anti-PLA2R and 24 h urine protein, and negatively correlated with total protein and serum albumin. Conclusions Plasma IL-21 levels increased significantly in patients with IMN. IL-21 may therefore serve as a biomarker for IMN.