Immunogenetic diversity of MHC Class II B-Lβ genes in Brazilian Caipiras (Free-Range) Chickens laying blue eggs

Carlos André da Veiga Lima Rosa Costamilan^1*Ediane Paludo²Marcos Edgar Herkenhoff^1*Fábio Pértille³André Luigi Soares de Souza²Carolina Rosai Mendes²Guilherme Dilarri^1*

• ¹Santa Catarina State University, Florianopolis, Brazil
• ²Universidade do Estado de Santa Catarina, Florianópolis, Brazil
• ³Uppsala Universitet, Uppsala, Sweden

The Brazilian "Caipira" (free-range) chickens that lay blue eggs represent a genetically diverse, non-commercial poultry population shaped by historical admixture with Araucana breeds. Despite their relevance for conservation and breeding programs, the immunogenetic characterization of these birds remains scarce. This study is the first to investigate the polymorphism of the MHC class II B-LβI and B-LβII genes in this ecotype. DNA from 100 blue-egg-laying Caipira chickens was analyzed. Based on exon 2 PCR profiles, 16 representative individuals were selected for cloning and sequencing. A total of 15 distinct nucleotide sequences were identified: eleven corresponding to the B-LβII gene and four to the B-LβI gene. Among them, five alleles (four B-LβII and one B-LβI) were novel and previously unrecorded in public databases. Comparative analysis revealed multiple nucleotide and amino acid substitutions across the alleles, particularly in polymorphic regions associated with antigen binding, while key functional sites such as the CHO-binding domain and disulfide bridges were conserved. These findings highlight the high immunogenetic variability of MHC class II loci in Caipira chickens and reinforce the potential role of these alleles in natural disease resistance. The study provides a foundational dataset for further investigations linking MHC variability to immune responsiveness and offers valuable insights for breeding strategies aiming to enhance disease resilience in poultry.