Proinflammatory cytokine mRNA expression in mammary tissue of sows following intramammary inoculation with Escherichia coli.

The expression of the proinflammatory cytokines interleukin-1beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor-alpha (TNF-alpha) mRNAs was determined by reverse transcription-PCR (RT-PCR) analysis of biopsies from the mammary glands of sows. The biopsies were collected before and 24h after intramammary inoculation of 12 pregnant sows with Escherichia coli (E. coli). Four of the sows developed clinical signs of mastitis and these animals displayed significantly lower levels of IL-1beta mRNA before inoculation than those that remained clinically healthy. There was a significant increase in IL-1beta, IL-6, IL-8, and TNF-alpha mRNA expression in the inoculated mammary glands of sows that developed clinical signs of mastitis (affected group) 24h postinoculation. This was also true for IL-8 and TNF-alpha mRNA expression in the inoculated mammary glands of sows that did not develop clinical signs of mastitis (non-affected group). No significant differences were found in IL-1beta, IL-6, and TNF-alpha mRNA expression in the inoculated mammary glands between groups (affected versus non-affected) 24h postinoculation. Thus, a local production of proinflammatory cytokines in the mammary gland of sows was indicated by the induced expression of IL-1beta, IL-6, IL-8, and TNF-alpha mRNAs after intramammary inoculation with E. coli.