Phenotypic, Functional, and Plasticity Features of Classical and Alternatively Activated Human Macrophages

Abdullah A. Tarique, Jayden Logan, Emma Thomas, Patrick G. Holt, Peter D. Sly, Emmanuelle Fantino

Macrophages are dynamic cells that mature under the influence of signals from the local microenvironment into either classically (M1) or alternatively (M2) activated macrophages with specific functional and phenotypic properties. While the phenotypic identification of M1 and M2 macrophages is well established in mice, this is less clear for human macrophages. In addition, the persistence and reversibility of polarized human phenotypes is not well established. Human peripheral blood monocytes were differentiated into macrophages (M0) and then polarized to M1 and M2 phenotypes using LPS/IFN-g and IL-4/IL-13, respectively. M1 and M2 were identified respectively as CD64+CD80+ and CD11b+CD209+ by flow-cytometry. Polarized M1 secreted IP-10, IFN-g, IL-8, TNF-a, IL-1b and RANTES while M2 secreted IL-13, CCL17 and CCL18. Functionally, M2 were highly endocytic. In cytokine deficient medium the polarized macrophages reverted back to the uncommitted M0 state within 12 days. If previously polarized macrophages were given the alternative polarizing stimulus after 6 day resting in cytokine deficient medium, a switch in polarization was seen, i.e., M1 macrophages switched to M2 and expressed CD11b+CD209+ and vice versa. In summary, we report phenotypic identification of human M1 and M2 macrophages, their functional characteristics and their ability to be re-programmed given the appropriate stimuli.