In vitro entry of neutrophils into mammary epithelial cells. Isolated fresh bovine blood neutrophils were placed on a monolayer of EPH-4 cells grown on glass cover slides in 24 wells culture plate. After 12 h cells were fixed with PFA and stained with Diff Quick and examined by bright light microscopy. Neutrophils (red arrows in A) adhere to EPH-4 cells (black arrows in A) before entry. Intraepithelial neutrophils (red arrows in B–D) are visible in a clear cytoplasmic vacuole indenting the nuclei of the host epithelial cell (black arrows in B–D). Some epithelial cells contain large numbers of intraepithelial neutrophils (C) while most contain one or two intraepithelial neutrophils (D). Scale bars 50 µm (A, B), and 50 µm (C, D). All images are representative of > 3 similar experiments.