An in vivo mammary infusion model for tissue migration of leucocytes during inflammation

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Abstract
Summary.: Infusion of LPS or nematode larvae into the mammary glands of sheep induces recruitment of neutrophils or eosinophils respectively. While neutrophil recruitment required only a single infusion of LPS, repeated infusions of parasite larvae were required to induce significant eosinophil migration into the lumen of the glands. Eosinophil recruitment was accompanied by a distinct population of lymphocytes consisting mainly of activated (MHC class II and CD25+) T cells. L‐selectin was expressed at reduced levels on both neutrophils and eosinophils collected from the mammary gland compared with cells present in the blood of the same sheep. In addition, VLA‐4 and β1‐integrin were down‐regulated or negative in mammary eosinophils compared with strong expression in the blood while neutrophils were negative for these markers in both mammary washes and blood. Eosinophils in blood and mammary glands were negative for MHC class II, CD25 and CD4. Mast cells and lymphocyte aggregates were present in the tissue of glands chronically stimulated with parasite larvae while eosinophils were only present if the gland had been recently stimulated.These studies show that detailed in vivo analysis of leucocyte migration can be easily performed in the sheep mammary infusion model which allows non‐invasive and repeated sampling of inflammatory cells before and after tissue migration.