Phenotypic characterization of monocyte subpopulations in the pig

We have recently described the existence of two subsets of porcine monocytes based on the expression of CD163. In this study we compare the expression of a number of cell surface antigens in CD163+ and CD163- monocyte subsets using three-color flow cytometry. These monocyte subsets show differences with respect to the expression of MHC class II antigens (SLA-DR and DQ) and a variety of adhesion molecules (CD11a, wCD11c, wCD29, CD49d) that are expressed at higher levels on CD163+ monocytes, and of CD14 that is higher expressed by CD163- cells. These differences on phenotype could reflect differences in the ability of these two subsets to migrate to tissues and may account for the higher allostimulatory capacity of CD163+ cells. In some aspects, the phenoype of CD163+ monocytes resembles that of mature macrophages. In vitro serum-induced maturation of monocytes into macrophages lead to the expression of SWC9 together with an increase in the expression of CD163 and a reduction in that of CD14. These results delineate a maturation pathway where CD14(hi)CD163-SWC9- monocytes develop into CD14(lo)CD163+SWC9- monocytes and these cells into CD14(lo)CD163+SWC9+ macrophages.