The acute-phase protein serum amyloid A3 is expressed in the bovine mammary gland and plays a role in host defence

Abstract

The serum amyloid A protein is one of the major reactants in the acute-phase response. Using representational difference analysis comparing RNA from normal and involuting quarters of a dairy cow mammary gland, we found an mRNA encoding the SAA3 protein (M-SAA3). The M-SAA3 mRNA was localized to restricted populations of bovine mammary epithelial cells (MECs). It was expressed at a moderate level in late pregnancy, at a low level through lactation, was induced early in milk stasis, and expressed at high levels in most MECs during mid to late involution and inflammation/mastitis. The mature M-SAA3 peptide was expressed in Escherichia coli, antibodies made, and shown to have antibacterial activity against E. coli, Streptococcus uberis and Pseudomonas aeruginosa. These results suggest that the mammary SAA3 may have a role in protection of the mammary gland during remodelling and infection and possibly in the neonate gastrointestinal tract.

Keywords::

• serum-amyloid-A3
• SAA3
• milk
• mammary
• antimicrobial
• bovine

Acknowledgements

This research was funded by the New Zealand Foundation for Research and Technology, and the Waikato Medical Research Foundation. We thank Prof. Richard Wilkins for suggesting the use of the RDA technique which found M-SAA3, Dr Harold Henderson for statistical analysis and Dr Tom Wheeler for critical reading of the text.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper