Expression profile of toll-like receptors within the gastrointestinal tract of 2-day-old Salmonella enteriditis-infected broiler chickens K.M. MacKinnon *, H. He, J.R. Nerren, C.L. Swaggerty, K.J. Genovese, M.H. Kogut USDA-ARS Southern Plains Agricultural Research Center, 2881 F&B Road, College Station, TX 77845, United States 1. Introduction The gram-negative bacteria, Salmonella enterica serovar Enteriditis (SE), causes a majority of foodborne illness in the U.S, and the number of cases has remained stable over the last 5 years (2008). The incidence of human infection can be limited by decreasing bacteria in poultry through the induction of avian immune mechanisms. Unfortu- nately, there is limited information on the function and distribution of many of the components comprising the avian immune response. In young chickens the innate immune response is particularly important since the acquired response does not fully develop until 1 week of age (Bar-Shira et al., 2003). A key component of the innate response is the pattern recognition receptors (PRRs), particularly the toll- like receptors (TLR) which recognize highly conserved structural motifs of certain microbes (Werling and Coffey, 2007). The following TLRs and their agonists are identified in chickens and are the focus of multiple reviews: TLR 1LA (also reported as 1 type 1, 1/6/10, and16) forms a dimer with TLR 2B; TLR 1LB forms a dimer with both TLR 2’s; TLR 2A, peptidoglycan and bacterial lipopeptides; TLR 2B, bacterial lipopeptides and lipopolysaccharide (LPS); TLR 3, double-stranded RNA and poly I:C; TLR 4, LPS; TLR 5, bacterial flagellin; TLR 7, possibly single-stranded RNA; TLR 8, is disrupted and has no known function; TLR 15, Veterinary Microbiology 137 (2009) 313–319 ARTICLE INFO Article history: Received 15 September 2008 Received in revised form 6 January 2009 Accepted 12 January 2009 Keywords: Toll-like receptor Gene expression Intestine Innate immunity Salmonella Bacteria Avian ABSTRACT 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. Published by Elsevier B.V. * Corresponding author. Tel.: +1 979 260 9388; fax: +1 979 260 9332. E-mail addresses: kathryn.mackinnon@ars.usda.gov, kmackinn@vt.edu (K.M. MacKinnon). Contents lists available at ScienceDirect Veterinary Microbiology journal homepage: www.elsevier.com/locate/vetmic 0378-1135/$ – see front matter . Published by Elsevier B.V. doi:10.1016/j.vetmic.2009.01.024