Monocytes and macrophages are critical regulators of the innate immune response. Classically activated macrophages (M1) are pro-inflammatory cells, which promote Th1 responses and tumoricidal activity. Alternatively activated macrophages (M2) have anti-inflammatory functions and elicit tissue repair, fibrosis, tumor growth and progression. We have developed off-the-shelf in vitro macrophage polarization assays using human primary blood derived cells to assess the translational potential of small molecules as novel therapies.
Blood-derived human CD14+ cells were cultured in presence of M-CSF for 5 days to accommodate differentiation into M0 macrophages, and subsequently treated with LPS or IL-4+IL-10 to induce polarization into M1 and M2. Inhibition of polarization was assessed by adding compounds one hour prior to induction of polarization and subsequent measurement of TNF-α secretion and CD80 expression as markers of M1 polarization and CCL-18 secretion and CD206 expression as markers of M2 polarization.
Exposure of M0 macrophages to LPS resulted in increased CD80 expression and TNF-α secretion. LPS-mediated TNF-α secretion is strongly inhibited by dexamethasone and prednisolone with consistent IC50 values across donors. Exposure of M0 macrophages to IL-4+IL-10 resulted in increased CD206 expression and CCL18 secretion. IL-4/IL-10-mediated CCL18 secretion is fully inhibited by tofacitinib with consistent IC50 value across donors.
Our data show that both the M1 and M2 polarization assays are robust and can serve as reliable tools for evaluating the potency and efficacy of prospective drugs in multiple diseases associated with classically or alternatively activated macrophages, such as fibrosis, rheumatoid arthritis, inflammatory bowel disease and cancer.