AB0007\u2005IL12B POLYMORPHISMS ARE ASSOCIATED WITH ELEVATED SERUM LEVELS OF IL-12P40, IL-23 AND GENETIC PREDISPOSITION TO RHEUMATOID ARTHRITIS

Abstract

Background Rheumatoid arthritis (RA) is the most common type of autoimmune arthritis in which genetic predisposition in close interaction with environmental triggers seems to be the major factor in the disease pathogenesis. Genetic analyses suggest a polygenic inheritance, as the largest genetic contribution to RA susceptibility remains the HLA–DRB1 gene, residing within the HLA gene complex. Since immune dysregulation plays a key role in immune-mediated inflammatory disorders, genetic variations within cytokine loci may contribute to variability in the immune response determining susceptibility or resistance to a certain autoimmune disease. Objectives We aimed to investigate whether IL12B polymorphisms are involved in causation of RA and in variations of circulating IL-23 and IL-12p40 levels in our Bulgarian population. Methods A total of 125 RA patients aged from 18 to 79 years in comparison to 239 age- and sex-matched healthy controls (HC) were genotyped for rs17860508 and rs3212227. Both IL12B polymorphisms were investigated by polymerase chain reaction (PCR) - based methods. Serum IL-12p40 and IL-23 concentrations measurement was done using ELISA test in 67 RA patients and 55 age-matched HC. Results An association between the rs17860508 polymorphism and RA development was established under the allelic model (allele 2 vs allele 1; OR = 1.68, 95%CI = 1.17–2.42, p = 0.0044), the co-dominant model (2.2 vs 1.1, OR = 2.83, 95%CI = 1.37–5.86; 1.2 vs 1.1 OR = 1.76, 95%CI = 0.91–3.41; p = 0.017), the dominant model (1.2 + 2.2 vs 1.1; OR = 2.12, 95%CI = 1.15–3.90, p = 0.014), and the recessive model (2.2 vs 1.1 +1.2; OR = 2.00, 95%CI = 1.10–3.62, p = 0.022). These results suppose that the homozygous 2.2 genotype could be predisposing, while 1.1genotype might be protective factor to RA susceptibility. No association between the rs3212227 and RA risk was revealed under the same genetic models. Also, a combined two loci model was designed with a referent group - the individuals with the IL12Bpro 1.1 + IL12 B 3’ UTR AA genotype. We found that the combination of IL12Bpro 1.1 with IL12B 3’ UTR AA genotype is protective factor for RA susceptibility, whereas the carriage of IL12Bpro allele 2 despite hetero- or homozygosity simultaneous with IL12B 3’ UTR AC/CC genotypes increase the RA risk more than 3-fold. The highest risk for RA susceptibility was established in the carriers of IL12B 3′ UTR allele C in combination with IL12Bpro 2.2 genotype, which was estimated to be 12.6 (95%CI = 2.478–71.412; p < 0.001). Circulating IL-12p40 and IL-23 levels were increased in the RA patients as a difference was observed depending on genotypes of rs17860508 and rs3212227. We found a functional effect of the rs3212227; the AA genotype was associated with a higher production of both IL-12p40 and IL-23 in RA cases, whereas the lowest serum levels were seen in CC genotype carriers. Also, the rs17860508 2.2 genotype, identified as a risk for RA, was associated with a higher serum levels of IL-23 in all patients. Notably, the highest circulating IL-23 levels were observed in carriers of the rs3212227 AA genotype and rs17860508 2.2 genotype compared to the remaining genotypes. Conclusion IL12Bpro (rs17860508) and 3’ UTR (rs17860508) polymorphisms does confer susceptibility to RA either as an individual or combinatorial effect and might influence the RA occurrence through regulating the expression of IL-12/IL-23 p40 and production of IL-23. Disclosure of Interests Mariana Ivanova Goycheva Speakers bureau: Abbvie, Pfizer, UCB, Novartis, Irena Manolova: None declared, Georgi Vasilev: None declared, Lyuba Miteva: None declared, Rumen Stoilov Speakers bureau: Abbvie, Pfizer, Amgen, UCB, Novartis, Spaska Stanilova: None declared