Interleukin-6 levels and their haplotypes are associated with serological autoantibodies status and clinical activity in rheumatoid arthritis

Our results show that the GGG haplotype of the IL-6 gene is associated with a serological status of double-positive autoantibodies [odds ratio (OR) = 2.09, p = 0.009], as well as with a double-positive high autoantibodies status (OR = 2.08, p = 0.04), although a marginal association was shown to RA susceptibility (OR = 1.34, p = 0.050). Polymorphisms and haplotypes were not associated with serum levels of IL-6. However, serum levels of IL-6 ≥27.6 pg/mL were associated with clinical features of RA severity, such as morning stiffness ≥30 min (OR = 1.83, p = 0.001), HAQ-DI ≥1 (OR = 2.73, p=0.009), DAS28-ESR ≥3.2 (OR = 3.63, p = 0.002), and hsCRP ≥10 mg/L (OR = 6.35, p < 0.001). This study provides evidence of the relationship between IL-6 haplotypes, circulating levels of IL-6, and clinical features and serological status to autoantibodies in patients with RA from Mexico.