Lipopolysaccharide and lipoteichoic acid induce different innate immune responses in bovine mammary epithelial cells

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The objective of the present study was to characterize the innate immune responses induced by in vitro stimulation of bovine primary mammary epithelial cells (bMEC) using gram-negative lipopolysaccharide (LPS) and gram-positive lipoteichoic acid (LTA) bacterial cell wall components. Quantitative real-time PCR (qRT-PCR) was employed to examine the mRNA expression of a panel of 22 cytokines, chemokines, β-defensins and components of the Toll-Like Receptor signaling pathway. Stimulation of bMEC with LPS for 24 h elicited a marked increase in mRNA expression for IL-1β, IL-8, TNFα, CXCL6 and β-defensin while members of the Toll-Like Receptor pathway, although present, were largely unaffected. Surprisingly, stimulation of these cells with LTA for 24 h did not significantly alter the expression of these genes. A time course of the expression of IL-1β, IL-8, TNFα, CXCL6 and β-defensin was subsequently performed. The mRNA levels of all genes increased rapidly after stimulation for 2–4 h with both LPS and LTA but only the former treatment resulted in sustained responses. In contrast, the increased gene expression for LTA stimulated cells returned to resting levels after 8–16 h with the exception of β-defensin, which remained up-regulated. The limited and unsustained cytokine response to LTA may explain why mastitis caused by gram-positive bacteria has greater potential for chronic intra-mammary infection than gram-negative infection. It was concluded that bovine mammary epithelial cells have a strong but differential capacity to mount innate immune responses to bacterial cell wall components.

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