Inducible and Constitutive In Vitro Neutrophil Chemokine Expression by Mammary Epithelial and Myoepithelial Cells

Previously, our laboratory showed that bovine and caprine mammary secretions are chemotactic and that chemoattractants found in these secretions are qualitatively different according to infection status and/or lactation stage. However, the cellular source of the chemoattractants has not been defined. In this study we used a modified Boyden chamber assay to examine the ability of previously established caprine mammary epithelial cell (CMEC) and myoepithelial cell (CMMyoEC) lines to produce chemoattractants for neutrophils. We found that CMEC culture supernatants, but not those of CMMyoEC cultures, induced in vitro neutrophil chemotaxis. Further characterization showed that chemotactic activity was produced when the cells underwent contact-induced differentiation. Neutrophil migration was chemotactic, not chemokinetic, and was augmented when the epithelial and myoepithelial cells were cocultured. Additionally, chemotactic activity was inducible by Staphylococcus aureus plus alpha-toxin, Escherichia coli, and interleukin-1beta (IL-1beta) in CMEC cultures. However, CMMyoEC cultures could not be induced to produce chemotactic activity. Anti-IL-8 antibody was able to block some constitutively produced chemotactic activity and chemotactic activity induced by IL-1beta and S. aureus plus alpha-toxin. These results indicate that epithelial cells may play a major role in producing chemoattractants, specifically IL-8, in the mammary gland.