Background Polymorphism of the PDCD1 gene are significantly associated with development of rheumatoid arthritis (RA), which may indicate the participation of the PD-1 (the programmed cell death 1) protein in the pathogenesis of the disease. There is a growing interest in the importance of the PD-1 in the maintenance of immunological balance and its role in the development of autoimmune diseases such as RA.

Objectives We estimate the incidence and association of polymorphic forms for PD-1 protein gene in patients with RA and healthy controls in the population of South-Eastern Poland.

Methods The distribution of genotypes in both patients' group (260 patients with RA) and the control group (100 subjects: 50 women and 50 men) were found to be Hardy-Weinberg equilibrium. In our study SNPs: PD-1.1 (rs36084323) G/A, PD-1.3 (rs11568821) G/A, PD-1.5 (rs2227981) C/T, PD-1.6 (rs10204525) G/A, PD-1.7 (rs41386349) C/T, PD-1.9 (rs2227982) C/T were examined by SNaPshot technique. Multiplex minisequencing reaction was performed with designed primers, basing on the sequences associated with 6 SNPs loci and with using kits ABI PRISM R SNAPShot ® Multiplex Kit (Applied Biosystems).The genotypes and the alleles of RA patients and the controls were analyzed by Fisher's exact test. Furthermore, the chi-square test and the Odds Ratio (OR) with Confidence Interval (CI) were computed for statistical analysis.

Results PD-1.5 C/T and PD-1.9 C/T polymorphisms affected the possibilities of RA occurrence in all the population. There was a significant difference in the distribution of genotype frequencies in RA patients compared with controls, for: SNP PD-1.5, with reduced frequency of CC genotype in RA patients (0.22 and 0.32 in those groups, p=0.0401), however SNP PD-1.9 frequency of CC genotype was higher in patients with RA when compared to the controls (0.99 and 0.94 in those groups, p=0.0160). The calculated odds ratio (OR) for RA patients having the CC genotyp of SNP PD-1.5 (versus CT or TT genotype) was 0,5785 (95% CI 0.3358-1.0049; p=0.0401;) and the p-value remained statistically significant. Thus the absence of homosygosity CC of SNP PD-1.5 affected the possibilities of RA occurrence. The calculated odds ratio (OR) for RA patients having the CC genotyp of SNP PD-1.9 (versus CT or TT genotype) was 5.4374 (95% CI 1.1343-34.2519; p=0.0160) and the p-value remained statistically significant. Thus the possession of homosygosity CC of SNP PD-1.9 affected the possibilities of RA development. We did not observe any significant difference in allele and genotype frequencies of PD-1.1 (rs36084323) G/A, PD-1.3 (rs11568821) G/A, PD-1.6 (rs10204525) G/A, PD-1.7 (rs41386349) C/T polymorphisms between the RA patients and the controls.

Conclusions In our study, we confirmed that homozygotes PD-1.5 CC and PD-1.9 CC are associated with RA occurrence. However, more genetic and immunological studies are needed to better explain the participation of the PD-1 protein in the autoimmune process.

Disclosure of Interest None declared