|Van Ryssen, B|
Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2009
Publication Date: 1/1/2010
Citation: Rinaldi, M., Li, R.W., Bannerman, D.D., Daniels, K.M., Clover, C.M., Silva, M.V., Paape, M.J., Van Ryssen, B., Burvenich, C., Capuco, A.V. 2010. A sentinel function for teat tissues in dairy cows: Dominant innate immune response elements define early response to E. coli mastitis. Functional and Integrative Genomics. 10(1):21-38. Interpretive Summary: Mastitis is one of the most costly diseases impacting the dairy industry worldwide and Escherichia coli bacteria are prominent mastitis pathogens. The objective of this study was to perform a thorough analysis of the early response to E. coli infection of the mammary gland. Response in tissues of the mammary gland from the teat to more internal structures of the gland was evaluated. We showed that intramammary infection with E. coli elicits wide-spread changes in gene expression and time-dependent differences in response between different regions of the infected gland. Past investigations have focused on the impact of mastitis on the secretory region within the bovine mammary gland. Our data provide strong support for an important immune surveillance role played by the teat. Tissues of the teat, including Furstenburg’s rosette and the teat cistern, appear to be sentinels and provide an important response during the early stage of intramammary infection. The gland cistern also responded quickly, whereas up-regulation of genes involved in inflammatory and immune protein pathways occurred later in secretory regions of the gland. Our results suggest that infiltrated immune cells and resident mammary cells, play an important role in recognition of pathogens and production of inflammatory mediators during mastitis. The contribution of each cell population remains unknown and further studies using methods that allow the isolation of cell populations, such as laser microdissection, may allow a clear assessment of the specific roles of infiltrated and resident mammary cells during mastitis.
Technical Abstract: Mastitis remains one of the most prevalent and costly diseases impacting the dairy industry worldwide. Escherichia coli is an environmental bacterium that frequently causes intramammary infections, the outcome of which depends on the capacity of the host to recognize and clear the bacterial pathogen. E. coli intramammary infection elicits localized and systemic responses, some of which have been characterized in mammary secretory tissue. However, nothing is known about early transcriptome-wide responses to infection that occur within regions of the teat and mammary parenchyma. Therefore, the objective of the current study was to use microarray analysis to characterize gene expression patterns and process networks that become activated in different regions of the mammary gland during the acute phase of experimentally induced intramammary infection with E. coli. Tissues evaluated were from Furstenburg’s rosette (FR), teat cistern (TC), gland cistern (GC), and lobulo-alveolar (LA) regions of control and infected mammary glands, 12 and 24 h after bacterial (or control) infusions. For selected genes, real-time quantitative reverse transcriptase PCR was performed to confirm the microarray findings (Toll-like receptors; TLR1, TLR2, TLR4, TLR6) and evaluate the correspondence between mRNA level in tissues and protein level in milk (interleukin 8, tumor necrosis factor-alpha, haptoglobin, lipopolysaccharide-binding protein). The main networks activated by E. coli infection pertained to immune and inflammatory response, with marked induction of genes encoding proteins that function in chemotaxis, leukocyte activation and signaling. Genomic response was greatest in tissues of the TC and GC at 12 h post-infection, while tissue of the LA region responded only, and most strongly of the regions, 24 h following the infection. Up-regulation of TLR2, TLR4, IL8, TNF-alpha and bactericidal/permeability-increasing protein peaked at 12 h post infection in tissues of the TC and in the GC, while the highest level of lipopolysaccharide-binding protein was reached at 24 h in the LA region of infected quarters. Very few genes were down–regulated within the time frame of this study. Similar genetic networks were impacted in all regions during early phases of E. coli intramammary infection, although regional differences throughout the gland were noted. Importantly, the tissues of the teat, which are first to encounter invading bacteria during a natural infection, responded rapidly and intensely, suggesting an important sentinel function for this region. Both resident mammary cells and infiltrating immune cells likely play an important role in recognition of pathogens and production of inflammatory mediators during mastitis.