Allelic diversity of Blec2 gene in indigenous and local chickens and red junglefowl in Thailand: Implications for disease resistance

Although selective breeding significantly enhances production traits in commercial chickens, it often compromises their immune function. Indigenous chickens, however, typically exhibit strong disease resistance. The major histocompatibility complex plays a critical role in the adaptive immune responses to pathogens in chickens. The Blec2 gene in the MHC-B region, which encodes a putative natural killer cell receptor, is a promising candidate that influences the early immune responses. Little, however, is known about polymorphisms of this gene in indigenous and local chicken breeds or red junglefowl in Thailand. In this study, polymorphisms in a partial fragment of exon 4 and intron 3 of Blec2 were examined using targeted next-generation sequencing and genetic diversity analyses. Fourteen alleles and nine single nucleotide substitutions were identified; these included both silent and missense mutations, which may influence immune function. Notably, one allele, Blec2*TH2, referred to as haplotype 21, is reported to be strongly associated with resistance against the H5N1 virus. Purifying selection alongside stochastic processes were also observed in this gene fragment, indicating a strong potential for disease resistance. By contrast, Blec2*TH13 allele referred to as haplotype 13, which was previously reported to correlate with 100% mortality rate for avian influenza, was detected in Nin Kaset breed. The study findings indicate the existence of diverse immune response mechanisms in indigenous and local chickens and red junglefowl in Thailand. These findings provide valuable insights that should be relevant for information for developing breeding programs using marker-assisted selection to enhance the immune resilience of commercial poultry stocks.