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

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 antiphospholipase 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.