Cloning and phylogenetic analysis of mature interleukin-18 gene in AA chicken

In this study, specific primers for chicken IL-18 cDNA had been designed and synthesized according to the published nucleic acid sequence of chicken IL-18 cDNA. The cDNA encoding chicken mature IL-18 was amplified by RT-PCR from RNA of chicken splenocytes stimulated with phytohemagglutinin and lipopolysaccharide. PCR product was cloned into pUCm-T vector and then was sequenced. The cloned fragment covered the whole mature IL-18 gene(507bp) and encoded 169 amino acids. The results of comparative sequence analysis indicated that putative amino acid sequence of the cloned IL-18 gene shared 96.5%～100% homology with IL-18 of chicken and turkey, and shared 20.1%～26.6% homology with mammalian IL-18. Phylogenetic tree analysis indicated that the chicken IL-18 have evolutionary relationship with mammalian IL-18, however they showed species difference in function because of selective pressure of immune systems. This study have paved the way for farther studying the expression and function of IL-18 as vaccine adjuvants