Phenotype of porcine monocytic cells: modulation of surface molecule expression upon monocyte differentiation into macrophages

When porcine blood monocytes differentiate in vitro into macrophages, their morphology, as well as side scatter and forward scatter measured by flow cytometry, changed in a manner similar to that with human cells. During this differentiation, the initial high expression of CD molecules on porcine monocytes was down-regulated, with one exception—SWC9. Freshly isolated blood monocytes were SWC9−, but after culture the cells had become SWC9+. Thus, porcine monocytes were characterised as SWC3+SWC9−CD14high; macrophages were SWC3+SWC9+CD14low, the latter also displaying a down-regulation of CD11a18, and, to a lesser degree, CD44. Both SWC9−CD14high monocytes and SWC9+CD14low macrophages were identifiable in freshly prepared monocytic cells from the spleen. Alveolar macrophages, on the other hand, were dominated by SWC9+CD14low cells, similar in phenotype to in vitro monocyte-derived macrophages. The consequences which these results have for studies on virus infections of porcine monocytic cells are discussed.