Association of IFN-γ Gene Polymorphisms with Avian Influenza-Related Immune Traits in Indonesian Local Chickens

Avian influenza (AI) remains a major threat to poultry production, and genetic improvement for disease resistance has emerged as a promising complementary strategy alongside vaccination and biosecurity measures. Interferon-gamma (IFN-γ) is a key cytokine involved in antiviral immunity; however, information regarding its genetic diversity and association with AI-related immune responses in Indonesian local chickens remains limited. This study aimed to identify single-nucleotide polymorphisms (SNPs) in the chicken IFN-γ gene and evaluate their associations with AI-related immune response traits. A total of 94 chickens, comprising IPB D1 (n = 60) and Merawangarab chickens (n = 34), were used. Blood samples were collected for DNA extraction, hematological analysis, quantification of immunoglobulin Y (IgY), and determination of avian influenza antibody titers. A 410 bp fragment of the IFN-γ gene was amplified and sequenced, revealing two SNPs located in exon 4, namely c.304C>G and c.390G>A. Genotype and allele frequencies were estimated, and association analyses were performed using a General Linear Model (GLM). Significant genotype effects were further compared using Tukey’s multiple comparison test. The C allele of c.304C>G and the G allele of c.390G>A were predominant in both chicken populations. Comparison of genotype distributions between populations revealed a significant difference for SNP c.304C>G (χ² = 8.713, p = 0.013), whereas no significant difference was observed for SNP c.390G>A (χ² = 3.784, p = 0.151). SNP c.304C>G was significantly associated with AI antibody titer, total leukocyte count, and eosinophil percentage, whereas SNP c.390G>A was significantly associated with AI antibody titer, total leukocyte count, heterophil percentage, and heterophil-to-lymphocyte ratio (p<0.05). These findings indicate that IFN-γ gene polymorphisms are associated with variation in AI-related immune responses in Indonesian local chickens and highlight IFN-γ as a candidate gene for marker-assisted selection to improve immune competence and disease resilience in poultry.