Interleukin-21 Is Associated with the Pathogenesis of Lumbar Disc Herniation

Inflammation is an important reaction underlying lumbar disc herniation (LDH). Th17 cells play a critical role in immune activation. Interleukin (IL)-21 controls the functional activity of effector T-helper cells and the differentiation of Th17 cells, and promotes B-cell differentiation. It plays important roles in chronic inflammation and autoimmune diseases. However, little is known about relationship between IL-21 and LDH. This study was aimed to determine the association between IL-21 levels and pain scores in LDH patients compared to healthy controls. We enrolled 34 LDH patients and 20 healthy controls in this study. The LDH patients underwent surgery. Pain intensity was recorded using visual analogue scale (VAS) scores preoperatively. Serum IL-21 and IL-17 levels in the peripheral blood were determined using enzyme-linked immunosorbent assay. Disc tissue was examined using western blot and quantitative reverse-transcription polymerase chain reaction to determine IL-21, IL-17, and cyclooxygenase (COX)-2 expression, and using immunohistochemistry to assess IL-21 expression. LDH patients exhibited significantly higher levels of serum IL-21 and IL-17 than healthy controls. Moreover, higher expression of IL-21, IL-17, and COX-2 was found in the protein and mRNA levels in disc tissues from LDH patients than in normal disc tissues. Different parameters like VAS pain scores, IL-17, and COX-2 were positively correlated with the IL- 21 levels. Enhanced production of IL-21 in disc tissues of LDH patients was also confirmed using immunohistochemical analyses. We concluded that inflammation was responsible for the pain associated with LDH, and that increased IL-21 expression may be associated with the pathogenesis of LDH.