Vet. Res. 37 (2006) 219-229
DOI: 10.1051/vetres:2005051

Characterization of cytokine expression in milk somatic cells during intramammary infections with Escherichia coli or Staphylococcus aureus by real-time PCR

Jai-Wei Lee^{a, b}, Douglas D. Bannerman^c, Max J. Paape^c, Ming-Kuei Huang^a and Xin Zhao<sup>a

a</sup>  Department of Animal Science, McGill University, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada
^b  Department of Tropical Agriculture and International Cooperation, National Pingtung University of Science and Technology, Neipu, Pingtung 91201, Taiwan
^c  Bovine Functional Genomics Laboratory, USDA-Agriculture Research Service, Beltsville, MD 20705, USA

(Received 29 May 2005; accepted 9 September 2005; published online 11 February 2006)

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)-, and interferon (IFN)-, by milk somatic cells was characterized by real-time polymerase chain reaction (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 (-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 demonstrated increased expression of a target gene and there was large variation among animals at each given time. As a consequence, most tested comparisons were not statistically significant 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 IFN-. The expression of IFN- 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, at least partially, 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.

Key words: mastitis / cytokine / Escherichia coli / Staphylococcus aureus / SCC

Corresponding author: Xin Zhao xin.zhao@mcgill.ca

© INRA, EDP Sciences 2006