| Summary: | <p>Abstract</p> <p>Background</p> <p>Bovine mastitis is one of the most costly and prevalent diseases affecting dairy cows worldwide. In order to develop new strategies to prevent <it>Escherichia coli</it>-induced mastitis, a detailed understanding of the molecular mechanisms underlying the host immune response to an <it>E. coli </it>infection is necessary. To this end, we performed a global gene-expression analysis of mammary gland tissue collected from dairy cows that had been exposed to a controlled <it>E. coli </it>infection. Biopsy samples of healthy and infected utter tissue were collected at T = 24 h post-infection (p.i.) and at T = 192 h p.i. to represent the acute phase response (APR) and chronic stage, respectively. Differentially expressed (DE) genes for each stage were analyzed and the DE genes detected at T = 24 h were also compared to data collected from two previous <it>E. coli </it>mastitis studies that were carried out on <it>post mortem </it>tissue.</p> <p>Results</p> <p>Nine-hundred-eighty-two transcripts were found to be differentially expressed in infected tissue at T = 24 (<it>P </it>< 0.05). Up-regulated transcripts (699) were largely associated with immune response functions, while the down-regulated transcripts (229) were principally involved in fat metabolism. At T = 192 h, all of the up-regulated transcripts were associated with tissue healing processes. Comparison of T = 24 h DE genes detected in the three <it>E. coli </it>mastitis studies revealed 248 were common and mainly involved immune response functions. KEGG pathway analysis indicated that these genes were involved in 12 pathways related to the pro-inflammatory response and APR, but also identified significant representation of two unexpected pathways: natural killer cell-mediated cytotoxicity pathway (KEGG04650) and the Rig-I-like receptor signalling pathway (KEGG04622).</p> <p>Conclusions</p> <p>In <it>E. coli</it>-induced mastitis, infected mammary gland tissue was found to significantly up-regulate expression of genes related to the immune response and down-regulate genes related to fat metabolism. Up to 25% of the DE immune response genes common to the three <it>E. coli </it>mastitis studies at T = 24 h were independent of <it>E. coli </it>strain and dose, cow lactation stage and number, tissue collection method and gene analysis method used. Hence, these DE genes likely represent important mediators of the local APR against <it>E. coli </it>in the mammary gland.</p>
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