Variability of the DRB locus of MHC genes class II in red deer (Cervus elaphus) from a mountain region of Croatia

Red deer (Cervus elaphus) are large indigenous mammals in Croatia. Even though Major Histocompatibility Complex (MHC) genes play a pivotal role in initiating immune response, there are no reports on their variability in red deer from Croatia. In this study, the variability of the DRB locus of MHC genes class II was analysed in 23 red deer from a mountain region of Croatia (Gorski Kotar). NGS sequencing revealed 23 unique DRB exon 2 sequences in 23 individuals, of which only six had been previously identified. The number of allelic variants per individual ranged from 1 to 6 (mean 3.09), with one individual having only one allele and one individual having all six allelic variants recognised. The most frequent allele, Ceel-DRB*HR01, was identified in 12 individuals (16.9%). The number of variable nucleotide sites was 84 (33.7%), and the number of variable amino acid positions in translated sequences was 44 (53%). The mean nucleotide evolutionary distance, based on the Jukes-Cantor model, with the gamma distribution shape parameter, was 16.5%, while the pairwise nucleotide distance ranged from 0.04% to 14.24%. The amino acid evolutionary distance, based on the Jones-Taylor-Thornton model, was 34.7%. Compared to the literature, it is clear that the mountain population of red deer from Croatia possesses considerable variability on the DRB locus, which is further confirmed by the notable nucleotide evolutionary distance.