Vaccine diluent affects expression levels of immune related genes in caecal tonsils of layer chickens vaccinated with live attenuated Salmonella Typhimurium vaccine

Typhimurium (ST) vaccine diluent effects on caecal tonsils gene regulation in layer chicks were investigated. A live attenuated ST vaccine was reconstituted in Marek's and/or water diluents, chicks vaccinated and caecal tonsils were assessed for global gene expression at days 7 and 14 post-vaccination. Differentially expressed genes (DEGs) involved in the activation of the intestinal immune network for IgA production were upregulated earlier (e.g. day 7 post-vaccination) in the water diluent group, while in the Marek's diluent group, this pathway was enriched by the upregulated DEGs at day 14 post-vaccination. The commonly upregulated biological pathways between the two diluents were cytokine-cytokine receptor interaction, toll-like receptor signaling pathway and cytosolic DNA-sensing pathway. At day 7 post-vaccination, 28.5% and 40.2% of the significantly upregulated genes were unique to Marek's and water diluents, respectively, whereas 31.3% were common between the Marek's and water diluent groups, showing the role of the diluent in priming the vaccine for host immune system modulation. At day 14 post-vaccination, 52.7% and 15.4% of the upregulated DEGs were unique to Marek's and water diluents, respectively. Overall, the data showed that the live attenuated ST vaccine reconstituted in Marek's diluent affected the regulation of immune system-related genes in the caecal tonsils of chicks, with a difference in pattern when water was used as a diluent.