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Title: CHARACTERIZATION OF CYTOKINE EXPRESSION IN MILK SOMATIC CELLS DURING INTRAMAMMARY INFECTIONS WITH ESCHERICHIA COLI OR STAPHYLOCOCCUS AUREUS BY REAL-TIME PCR

Author
item WEI-LEE, JAI - MCGILL UNIVERSITY
item Bannerman, Douglas
item Paape, Max
item HUANG, MING-KUEI - MCGILL UNIVERSITY
item ZHAO, XIN - MCGILL UNIVERSITY

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2005
Publication Date: 3/1/2006
Citation: Wei-Lee, J., Bannerman, D.D., Paape, M.J., Huang, M., Zhao, X. 2006. Characterization of Cytokine Expression in Milk Somatic Cells During Intramammary Infections with Escherichia Coli or Staphylococcus Aureus by Real-Time PCR. Veterinary Research. 37(2):219-229.

Interpretive Summary: The ability of bacteria to establish infection is due to both intrinsic properties of the pathogen, itself, and the nature of the host immune response to the bacteria. This study characterized the immune response elicited in response to intramammary infection with Escherichia coli and Staphylococcus aureus, the most prevalent environmental and contagious mastitis pathogens, respectively. The present report identifies differential cytokine expression patterns that result in successful clearance of a pathogen or the development of a chronic infection. This study provides the basis for the development of interventions that can mimic the cytokine response that leads to host eradication of an intramammary bacterial pathogen.

Technical Abstract: The expression of inflammatory cytokines, including interleukin (IL)-6, IL-8, IL-12, granulocyte macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor (TNF)-a, and interferon (IFN)-g, by milk somatic cells was characterized by real-time PCR in dairy cows experimentally challenged with either E. coli (n = 8) or S. aureus (n = 8). The mRNA abundance of a target gene was calibrated with that of a reference gene (beta-actin) and expressed as fold of induction over the control quarter at each time point. At no single time point did all eight quarters challenged with the same type of bacteria demonstrate increased expression of a target gene, thus there was large variation among animals at each given time. As a consequence, most tested comparisons were not statistically significant (P > 0.05), except the peak time points of IL-8 expression (75- and 29- fold in glands challenged with E. coli and S. aureus, respectively). However, the average fold induction of all targeted cytokines was increased in response to both bacterial challenges with the exception of IFNg. The expression of IFN-g was only increased in milk somatic cells isolated from E. coli, but not S. aureus, challenged mammary glands. Moreover, upregulated expression of cytokine genes had higher magnitudes and/or faster responses in glands challenged with E. coli in comparison with those challenged with S. aureus. We propose that the compromised upregulation of inflammatory cytokines in S. aureus infected glands may contribute to the chronic course of infection caused by this pathogen. Further research on identifying factors responsible for the differentially expressed cytokine profiles may be fundamental to developing strategies that mitigate the outcome of bovine mastitis.