Abstract
Bovine respiratory disease is a complex of bacterial and viral infections of economic and welfare importance to the beef industry. Although tracheal antimicrobial peptide (TAP) has microbicidal activity against bacterial pathogens causing bovine respiratory disease, risk factors for bovine respiratory disease including BVDV and stress (glucocorticoids) have been shown to inhibit the induced expression of this gene. Lipopolysaccharide is known to stimulate TAP gene expression, but the maximum effect is only observed after 16 h of stimulation. The present study investigated other agonists of TAP gene expression in primary cultures of bovine tracheal epithelial cells. PCR analysis of unstimulated tracheal epithelial cells, tracheal tissue and lung tissue each showed mRNA expression for Toll-like receptors (TLRs) 1–10. Quantitative RT-PCR analysis showed that Pam3CSK4 (an agonist of TLR1/2) and interleukin (IL)-17A significantly induced TAP gene expression in tracheal epithelial cells after only 4–8 h of stimulation. Flagellin (a TLR5 agonist), lipopolysaccharide and interferon-α also had stimulatory effects, but little or no response was found with class B CpG ODN 2007 (TLR9 agonist) or lipoteichoic acid (TLR2 agonist). The use of combined agonists had little or no enhancing effect above that of single agonists. Thus, Pam3CSK4, IL-17A and lipopolysaccharide rapidly and significantly induce TAP gene expression, suggesting that these stimulatory pathways may be of value for enhancing innate immunity in feedlot cattle at times of susceptibility to disease.
Highlights
Tracheal antimicrobial peptide is an inducible β-defensin that is highly expressed in the bovine respiratory tract and has demonstrated antimicrobial effects on pathogens that cause bovine respiratory disease, including Mannheimia haemolytica, Histophilus somni and Pasteurella multocida [1,2,3]
Effect of agonists on tracheal antimicrobial peptide (TAP) gene expression TAP gene expression was measured in bovine tracheal epithelial cells (bTEC) stimulated with Toll-like receptor (TLR) agonists and cytokines
Pam3CSK4, an agonist of the TLR2/1 heterodimer, induced TAP gene expression in a dose-dependent manner from 31.6 ng/mL to a maximal effect at the highest dose tested of 3.16 μg/mL
Summary
Tracheal antimicrobial peptide is an inducible β-defensin that is highly expressed in the bovine respiratory tract and has demonstrated antimicrobial effects on pathogens that cause bovine respiratory disease, including Mannheimia haemolytica, Histophilus somni and Pasteurella multocida [1,2,3]. The susceptibility of bovine bacterial pathogens to TAP suggests that restoring this. The induction of TAP gene expression by LPS is delayed and does not reach zenith until 16 h of stimulation, perhaps suggesting indirect signal transduction. The purpose of this study was to determine which TLR receptors are constitutively expressed by bovine tracheal epithelial cells, and to identify agonists that induce high levels of TAP gene expression more rapidly than LPS. Toll-like receptor (TLR) ligands were a focus of the study, including lipoteichoic acid (TLR2/2), Pam3CSK4 (TLR2/1), FSL-1 (TLR2/6), LPS (TLR4), flagellin (TLR5), and CpG ODN 2007 (TLR9). We examined IL-17A because of its emerging recognition as a critical stimulus for mucosal defence against bacterial infection, and interferon (IFN)-α because of the commercial availability of an immunostimulant (inactivated Parapoxvirus ovis, Zylexis) known to induce its expression [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
