Whole transcriptome response of chicken spleen and peripheral blood leukocytes to avian pathogenic Escherichia coli

A greater understanding of the immune response after infection can form the necessary foundation of knowledge needed to enhance immunity through genetic selection. Whole genome microarrays allow for comprehensive analysis of the transcriptome. The transcriptomic responses of spleen and peripheral blood leukocytes (PBL) each displayed differential expression in broiler chickens infected with avian pathogenic Escherichia coli (APEC), the causative agent for colibacillosis. This differential expression was associated with treatment factors of infection status, pathology level and day post-infection. Within the spleen, the largest number of significantly differentially expressed genes was between chickens with a severe pathology and those uninfected: 1,101 genes at 1 day post-infection and 1,723 genes at 5 days post-infection. Significant differences in splenic expression between mild and severe pathology was only noted at 5 days post-infection, for 799 genes. Within PBL, the largest number of significantly differentially expressed genes was between mild and severe pathology on day 5, for 1,914 genes. Significant differences in expression were also noted between severe pathology and uninfected chickens, for 1,097 genes at 1 day post-infection and for 506 genes at 5 days post-infection. In both tissues, a severe pathological state resulted in more induction of gene expression response than repression. Several immune-related gene families, including the Toll-like receptors, cytokines and beta-defensins, were differentially expressed in both tissues. Combining results from the two tissues revealed potential pathway regulation between tissues over time. MAPK pathway signaling in PBL at 1 day post-infection, could be causative for the downstream cytokine and p53 pathway signaling observed in the spleen at 5 days post-infection. Vaccination against an APEC virulence factor generated no discernible difference in gene expression in either tissue, with or without other factors of day, challenge, or pathology, although it was efficacious in reducing pathology, indicating further research is necessary to identify the impact of APEC vaccination on the transcriptome. Combining this knowledge with genotypic markers could help to reveal the genomic locations responsible for conveying APEC resistance, allowing breeders to use this information to reduce the incidence of APEC infection in poultry