The role of interleukin 4 and IL-4RA in intervertebral disc degeneration: investigation of single nucleotide polymorphisms in genes and a systematic review & meta-analysis of IL-4 expression level.

Intervertebral disc degeneration (IVDD) is a multifactorial disease that is sensitive to the balance between anti-inflammatory and pro-inflammatory cytokines. This study investigated the single nucleotide polymorphisms (SNPs) of interleukin 4 (IL-4) in IVDD. Genomic DNA of peripheral mononuclear cells of 76 IVDD patients and 140 healthy controls were investigated for three SNPs of IL-4 (rs2243248 (-1098G/T), rs2243250 (-590 C/T), rs2070874 (-33 C/T)) and 1 SNP of IL-4RA (rs180275, +1902 A/G) through PCR-SSP method. The 'C' allele frequency of IL-4 rs2243250 was 104 in 76 patients, while it was 149 in 140 controls (OR = 2,  = .001); also this SNP was significantly associated with post-operative pain reduction. The 'C' allele of IL-4 rs2070874 (130 in 76 patients, and 200 in 140 controls, OR = 2.66), and the 'CC' genotype were more frequent among patients (OR = 3.98,  < .001) than controls. 'TTT' haplotype was more common in controls (OR = 0.36,  < .001) and 'TCC' was also more common in patients (OR = 1.75,  = .012). A meta-analysis of previous studies found significantly higher IL-4 levels in disc tissues of IVDD patients, which was not similarly found in blood samples. The immune system plays an important role in IVDD. The extent and progress of the disease vary significantly with IL-4 level. Meanwhile, the rs2070874 and rs2243250 SNPs of IL-4 were significantly associated with IVDD in Iranian patients.