Stimulating innate immunity in feedlot cattle: strategies to induce tracheal antimicrobial peptide gene expression

Abstract

Tracheal antimicrobial peptide (TAP) is a β-defensin with microbicidal activity against bacterial pathogens causing bovine respiratory disease. Lipopolysaccharide stimulates TAP gene expression, with maximal effect after 16 hours of stimulation. This study investigated other agonists of TAP gene expression to enhance immunity in calves during times of increased disease risk. Unstimulated bovine tracheal epithelial cells grown in culture expressed mRNA for IL-17RA and Toll-like receptors (TLR) 1-6 and 9. These cells were stimulated with agonists and TAP gene expression was measured by quantitative RT-PCR. Pam3CSK4 (a TLR2/1 agonist) and IL-17A significantly induced TAP gene expression after only 8 hours of stimulation. Flagellin (TLR5 agonist), and IFN-α also had stimulatory effects after 16 hours of stimulation, but little or no response was found with CpG-ODN (TLR9 agonist) or lipoteichoic acid (TLR2/2 agonist). Therefore, IL-17A and TLR2/1 agonists may be of value to stimulate innate immunity in immunosuppressed feedlot cattle.