Candidate Gene Approach: Potentional Association ofCaspase‐1,Inhibitor of Apoptosis Protein‐1, andProsaposinGene Polymorphisms with Response toSalmonella enteritidisChallenge or Vaccination in Young Chicks

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Abstract
Salmonella enteritidis (SE) contamination of poultry products is a major cause of foodborne disease worldwide. Caspase-1 and inhibitor of apoptosis protein-1 (IAP-1) were selected as candidate genes for chicken response to SE because their proteins play critical roles in the apoptotic pathway when intracellular bacteria interact with host cells. Prosaposin (PSAP) was selected as a positional candidate gene based on a previous quantitative trait loci (QTL) linkage study using the same population. The F1 offspring of outbred sires crossed with three diverse, highly inbred dam lines (two major histocompatibility complex-congenic Leghorn lines named G-B1 and G-B2, and one Fayoumi line) were used to define the phenotypes. The F1 birds were involved in either pathogenic SE challenge, in which spleen and cecum content bacterial load were quantified, or SE vaccination, in which plasma antibody level to SE vaccine was evaluated. A polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) assay was developed to identify single-nucleotide polymorphism (SNP) in the three genes. The F1 offspring of heterozygous sires for each gene were genotyped. The sire caspase-1 gene was significantly associated with cecum content bacterial load (P = 0.04) in the three combined dam line crosses, and with spleen bacterial load in the G-B1 cross (P=0.02). The sire caspase-1 gene was also significantly associated with antibody level to SE vaccine (P=0.03) in F1 males in the three combined dam line crosses. The sire IAP-1 gene was significantly associated with spleen bacterial load (P=0.04) in the three combined dam-line crosses, and interacted with dam-line genetics (P = 0.01) for cecum content bacterial load. The sire PSAP gene significantly interacted with sex for spleen bacterial load (P = 0.004). This study is the first to demonstrate the association of SNPs for caspase-1, IAP-1, and PSAP genes with SE vaccine and with pathogen challenge response in chickens.