Accumulation of leucocytes and cytokines in the lactating ovine udder during mastitis due to Staphylococcus aureus and Escherichia coli.

The accumulation of leucocytes in milk and in teat cistern tissues, and the presence of the cytokines interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma) in milk was studied during inflammation in the lactating ovine udder induced by Staphylococcus aureus and Escherichia coli. Milk and/or teat tissue samples were taken before and four, eight and 24 hours after inoculation. Both S aureus and E coli induced a significant accumulation of leucocytes in milk, S aureus from eight hours with a peak after 24 hours, and E coli from four hours, with a peak after eight hours. After the inoculation of S aureus the numbers of subepithelial neutrophils in the teat cistern tissues were increased after four hours and had increased further by eight hours. After the inoculation of E coli, tissue neutrophil numbers peaked at four hours and were still high at eight hours. Large numbers of S aureus were recovered from milk throughout the experiments whereas the recovery of E coli diminished over time. TNF-alpha, IL-8 and IL-1 beta were detected in milk during the inflammation, and low levels of GM-CSF and IFN-gamma were also observed occasionally. Of the cytokines measured, TNF-alpha and IL-8 reached the highest concentrations, accumulating in a similar pattern to the leucocytes for both infections. IL-1 beta was detected mainly during S aureus-induced inflammation, indicating differences in the inflammatory responses elicited by the organisms.