Immunogenetics Properties of Avian MHC Polymorphism and its Association with Diseases and Production Traits

Abstract

Avian immunogenetics has emerged as a critical field in understanding the genetic basis of disease resistance and immune competence in poultry. Though structurally simpler than its mammalian counterpart, the Major Histocompatibility Complex (MHC) in chickens plays a pivotal role in pathogen defense due mainly to MHC’s high polymorphism and dominant allelic expression patterns. Unlike mammals, where MHC class I and II molecules exhibit co-dominant expression, chickens predominantly express a single MHC class I molecule, leading to a binary resistance/susceptibility outcome against specific pathogens; their polymorphisms influence not only immunity but also economically valuable traits (i.e., growth and egg production). This unique feature has facilitated extensive research linking MHC alleles to disease outcomes, including resistance to infectious bursal disease virus (IBDV), Marek’s disease (MD), and avian influenza. Beyond immunity, MHC polymorphisms correlate with economically significant traits such as egg production and growth rates, underscoring their dual role in health and production. However, modern poultry breeding programs often overlook genetic diversity, prioritizing production traits at the expense of immunocompetence. Integrating MHC-based marker-assisted breeding into poultry programs is essential to preserve genetic diversity and enhance immunocompetence. By leveraging advances in genomics and immunogenetics, future research can optimize poultry health, ensuring sustainable production in the face of evolving pathogen threats. This review highlights the importance of MHC polymorphism for both disease management and poultry economics; particularly, the study’s strength lies in its presentation of allele-specific immunocompetence patterns across viral, bacterial, and parasitic pathogens, easing integrating MHC-based marker-assisted selection into breeding strategies to enhance disease resistance while maintaining genetic variability. These insights advance avian immunology and offer practical applications for improving global poultry welfare and food security.