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

The expression of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, IL-8, and tumor necrosis factor-α (TNF-α) mRNAs was determined by reverse transcription-PCR (RT-PCR) analysis of biopsies from the mammary glands of sows. The biopsies were collected before and 24 h 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-1β mRNA before inoculation than those that remained clinically healthy. There was a significant increase in IL-1β, IL-6, IL-8, and TNF-α mRNA expression in the inoculated mammary glands of sows that developed clinical signs of mastitis (affected group) 24 h postinoculation. This was also true for IL-8 and TNF-α 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-1β, IL-6, and TNF-α mRNA expression in the inoculated mammary glands between groups (affected versus non-affected) 24 h postinoculation. Thus, a local production of proinflammatory cytokines in the mammary gland of sows was indicated by the induced expression of IL-1β, IL-6, IL-8, and TNF-α mRNAs after intramammary inoculation with E. coli.