Association of polymorphisms in the human IL-10 and IL-18 genes with rheumatoid arthritis

The decrease of anti-inflammatory cytokine and increase of pro-inflammatory cytokine was observed in rheumatoid arthritis (RA). Interleukin-10 (IL-10), a potent anti-inflammatory cytokine, has been demonstrated to suppress joint swelling and deformation in RA animal model. Interleukin-18 (IL-18), a widely distributed pro-inflammatory cytokine, induces the production of IFN-gamma, activate NK cells, and promote inflammation. Recent studies demonstrated that the serum IL-10 and IL-18 levels may be influenced by genetics and related to susceptibility to several autoimmune diseases. In the present study, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing techniques, we analyzed the genotype and allele distributions of two single nucleotide polymorphisms (SNP) loci in the promoter region of IL-10 and IL-18 genes (IL-10-592 A/C and IL-18-607 A/C loci, respectively). Our results indicated that IL-10-592 allelic and genotypic frequencies were significantly different between the RA patients and normal subjects (P < 0.05). In addition, significant differences of IL-10-592 allelic and genotypic frequencies were also detected between the patients with or without anti-cyclic citrullinated peptide antibody (anti-CCP) (P < 0.05). In contrast, allelic and genotypic frequencies of IL-18-607 did not show significant difference between RA patients and normal subjects (P > 0.05) or between anti-CCP-positive and anti-CCP-negative RA patients (P > 0.05). Furthermore, ELISA detection of IL-10 and IL-18 serum levels revealed that the genotype of IL-10-592 was associated with IL-10 serum level (P < 0.05), but the genotype and allele frequency of IL-18-607 was not associated with IL-18 serum level (P > 0.05). Taken together, our findings provide new insight for the polymorphism of IL-10 gene in the pathogenesis of RA.