Escherichia coli inoculation of porcine mammary glands affects local mRNA expression of Toll-like receptors and regulatory cytokines

The expression of mRNAs for the Toll-like receptors (TLRs) TLR2 and TLR4, pro- and anti inflammatory cytokines and their receptors was evaluated in mammary gland biopsy material collected from sows intramammarily inoculated with Escherichia coli strain O127 at parturition. Quantitative real-time RT-PCR analysis showed increased mRNA levels for TLR2, the proinflammatory cytokines interleukin IL-1β and tumor necrosis factor-alpha TNF-α, and the anti-inflammatory cytokine IL-10 in the inoculated mammary glands 24 h after inoculation. Increased mRNA levels of the proinflammatory cytokine IL-6 were only observed in the inoculated mammary glands of sows that developed clinical signs of mastitis. In contrast, the expression of the anti-inflammatory cytokine, transforming growth factor-beta 1 (TGF-β1) mRNA was unaltered, as was mRNA expression for the IL-1 receptor type I (IL-1R1). Furthermore, IL-1β and IL-10 mRNA expression was higher in the inoculated mammary glands of sows that developed clinical signs of mastitis compared with sows that remained clinically healthy. Notably, sows that developed clinical signs of mastitis had significantly lower pre-inoculation levels of IL-1β mRNA than sows that remained clinically healthy. These findings suggest that development of coliform mastitis is associated with the level of local expression of regulatory cytokines in response to intramammary E. coli inoculation and infection.