Interleukin – 6 Serum Level and Single Nucleotide Gene -174 G/C promoter Polymorphism in Patients with Rheumatoid Arthritis / Iraq

Objective: To 1) assess IL-6 levels in the serum of patients with rheumatoid arthritis (RA). 2) study IL-6 promoter -174 G>C single nucleotide polymorphism (SNP) as an imminent factor for the disease development. 3) find any relation between the level of serum IL-6 cytokine and other parameters such as age, gender, clinical severity of diseases and disease activity scores (DAS28). Materials & methods: This research was carried out through a case control approach at Ibn Senna Teaching Hospital in Mosul city between November 2020 and July 2021. It included 61 RA patients diagnosed according to ACR / EULAR 2010 criteria and 50 healthy individuals. IL-6 serum levels were ascertained by ELISA and genotyping of IL-6 promoter was accomplished by sequence-specific primer-polymerase chain reaction (SSP-PCR). Results: Mean IL-6 level in RA (69.42 ng /l 62.99) was elevated in comparison to healthy people (14.66 ng /l 23.58), P < 0.001. No age or gender effects on IL-6 concentration were noted. The ideal cut-off of IL-6 for discrimination of RA with best discriminative utility compared to healthy controls was 22.80 ng/l. At this value the IL-6 sensitivity was 91.8%, specificity 82.0% and accuracy rate 73.80%. G/G genotype was the most pervasive genotype in both RA patients and controls (70.5% in RA and 64% in healthy controls). However, it did not seem to be a risk factor for RA development compared to G/C or C/C genotypes (OR = 1.3438, 95% CI=0.605-2.984,P=0.469). The mean IL-6 level in patients with GG genotype was (73.70 ng / l 71.09) compared to (58.37 ng /l 37.86) in patients with GC genotype. There was no significant difference in the IL-6 level between patients with GG and patients with GC genotypes (P = 0.2375). Although higher IL-6 mean concentration was reported in severe RA, however, no significant difference was found between patients with mild, moderate and severe RA respectively. No correlation of serum levels of IL-6 with genetic promoter polymorphism, clinical severity of diseases or DAS 28 score were reported. Conclusion: The concentration of serum IL-6 was elevated in RA in regard to healthy controls which confirmed its pivotal role in RA pathogenesis. Our data did not support the role of IL-6 promoter -174 G> C polymorphism as a risk factor for RA, nor seem to play a major role in the increase of IL-6 level among our patients with RA.