Reprograming Model of Human Monocyte-derived Macrophages for <em>In-vitro</em> Assays

Cells of the monocyte-macrophage lineage are multifunctional and found in almost all body tissues. They coordinate innate and adaptive immunity´s initiation and resolution phases, significantly affecting protective immunity and immune-mediated pathological injury. While tissue-resident macrophages are key players in maintaining homeostasis in a steady state, large amounts of monocytes are recruited from the peripheral blood into the tissue following damage or inflammatory insults. Monocyte-derived macrophages (M-DM) can differentiate into many dynamic subtypes, and their phenotypes and functions depend on the local tissue environment. To compare different stimuli or environmental conditions during M-DM differentiation and polarization, we standardized an in-vitro model of human nonpolarized M-DM M0 and some cardinal cytokine-polarized macrophages, IFNγ/LPS-derived M1, IL-4-derived M2a, and IL-10 or dexamethasone-derived M2c, to analyze skewing reprogramming of M-DM by flow cytometry and real-time PCR. We found that CD64, CD206, CD163, CD14, and MERTK can clearly discriminate unpolarized M0 and polarized M1, M2a, and M2c by flow cytometry. Moreover, we defined IRF1 and CXCL10 as specific genes for classical IFNγ/LPS-derived M1-, IRF4-, CCL22-, and TGM2-specific transcripts for IL-4-derived M2a, and the MERTK gene for dexamethasone-derived M2c. To summarize, our standardized M-DM protocol could give the cardinal in-vitro map to analyze the differentiation and polarization of human M-DM under diverse stimuli.