Expression profile of toll-like receptors within the gastrointestinal tract of 2-day-old Salmonella enteriditis-infected broiler chickens.

Salmonella enterica serovar Enteriditis (SE) causes a majority of foodborne illness in the U.S. A more productive avian innate immune response could reduce bacterial colonization and the incidence of infection in humans. However, quantification and comparison of the toll-like receptors (TLR), a component of the innate immune system that recognize bacterial pathogens, and their response to SE colonization across the avian gastrointestinal (GI) tract has not been reported. Therefore, we assessed these changes using real-time qRT-PCR to measure expression of TLR 1LA, 2A, 2B, 3, 4, 5, 7, 15, and 21 in the duodenum, jejunum, ileum, cecal tonsil, ceca, and large intestine of uninfected and SE-infected 2-day-old broiler chickens. Samples were collected soon after hatch to approximate natural SE exposure and to measure initial changes in the immune response to infection. All TLRs had measurable expression within the duodenum, jejunum, ileum, cecal tonsil, ceca, and large intestine. The general expression pattern, with the exception of TLR 21, showed distal GI segments had higher TLR mRNA expression than proximal segments. Infected chickens had increased expression of TLR 1LA, 2A, 4, and 15 in distal GI segments and upregulation of TLR 2B, 3, and 15 in proximal segments, including the duodenum. Interestingly, SE-infection caused downregulation of TLR 5, with no change in TLR 7 or 21. Overall, we provide a comprehensive report of mRNA expression profiles for the TLR family of innate immune receptors in the GI tract of 2-day-old broilers and their differential response to SE colonization.