TLR5 ligand induces the gene expression of antimicrobial peptides and CXCL8 through IL-1β gene expression in cultured rumen epithelial cells

High grain feeding or weaning, which could compromise the rumen epithelium by increasing ruminal short-chain fatty acid (SCFA) concentrations with pH reduction, is associated with high levels of ruminal toll-like receptor 5 (TLR5). This study aimed to determine the role of TLR5 in the rumen epithelium. Immunohistochemistry revealed that TLR5 was localized in cells on the basal side (i.e., basal and spinous layers) rather than in the granular layer in the rumen epithelium, where tight junctions are most potent, in pre- and post-weaning calves (n = 9). Primary bovine rumen epithelial cells (BRECs) obtained from Holstein cows (n = 3) were cultured to investigate the factors that upregulate TLR5; however, SCFA, low pH (pH 5.6), BHBA, L-lactate, D-lactate, and LPS did not upregulate TLR5 gene expression in BREC. Primary BREC treated with flagellin (TLR5 ligand) had higher expression of interleukin-1β (IL-1β) (P < 0.05) than BREC treated with vehicle. In addition, BREC treated with IL-1β had higher expression of antimicrobial peptides and C-X-C motif chemokine ligand 8 than BREC treated with vehicle (P < 0.05). These results suggest that ruminal TLR5 may recognize epithelial disruption via flagellin and mediate the immune response via IL-1β during high-grain feeding or weaning.