Classically or alternatively activated bovine monocyte-derived macrophages in vitro do not resemble CD163/Calprotectin biased macrophage populations in the teat.

The functional phenotype of resident macrophages significantly determines the character of an inflammatory response. In this study we identified two phenotypes of tissue macrophages in bovine teat tissue based on expression of Calprotectin and CD163. To investigate a possible link between the dichotomy in phenotype and functional properties of cells in association with different host mediators we set up an in vitro model with bovine monocyte-derived macrophages (MdM). In vitro differentiated MdM invariably and uniformly expressed both antigens. Classically activated MdM (IFN-γ priming and LPS stimulation) showed a decreased CD163 expression while alternative activation (IL-4/IL-13 priming) did not change expression of CD163 and Calprotectin. Differently activated MdM showed a clearly distinct expression of genes related to classical (IL-12, inducible NO synthase) or alternative activation (IL-10, arginase I). The presence of the inflammatory host mediator prostaglandin E(2) (PGE(2)) neither influenced expression of Calprotectin and CD163 nor gene expression profiles in MdM generated in the presence of PGE(2) (PGE(2)-MdM). Supernatants of PGE(2-)MdM, however, significantly dampened the migration of neutrophilic granulocytes. The results of this study highlight the discrepancy between in vivo and in vitro obtained macrophages and point to the necessity to analyze the functional capacities of bovine tissue macrophages in situ.