Genetic evidence for the existence of interleukin-23 and for variation in the interleukin-12 and interleukin-12 receptor genes in the horse

Immune loci, characterized by features reflecting their role in defense reactions and consequently related to evolutionary mechanisms, including polymorphisms or association with disease are suitable candidates for comparative analysis. Interleukin-12 and related cytokines are key molecules regulating natural and specific immune responses. In this study, we analyzed four horse IL12-related genes: IL23p19, IL12Rβ2, IL12p40, and IL12p35. Genomic nucleotide sequence of the horse IL23 p19 sub-unit encoding gene was determined. The horse IL23p19 gene consists of four exons; its total mRNA length is 1004 bp, with a coding region of 579 bp. The predicted amino acid sequence of the horse IL23p19 sub-unit showed 88.0% sequence identity with the human sequence. A partial genomic sequence highly homologous to human IL12Rβ2 suggesting existence of this gene in the horse was retrieved. Single nucleotide polymorphisms (SNPs) were identified in all four genes analyzed. PCR-RFLP genotyping was developed for selected SNPs. Inter-breed differences in allele and genotype frequencies were observed in IL12p35 SNP 242. The results showed that horse IL12-related genes are comparable to their counterparts in other mammalian species in terms of their structure and their genetic variation.