An optimized Protocol for Human M2 Macrophages using M‐CSF and IL‐4/IL‐10/TGF‐β Yields a Dominant Immunosuppressive Phenotype

Monocytes are highly abundant circulatory effector cells and play a vital role in driving or resolving inflammatory processes depending on their activation phenotype. We investigated and compared a panel of polarization protocols of blood‐derived monocytes to achieve a stable, optimal and effective regimen for in vitro induction of immunosuppressive human macrophages, evaluating their surface receptor expression, cytokine profile, scavenging function and ability to suppress T‐cell proliferation. Importantly, we assessed the effect of copolarization or secondary pro‐inflammatory stimulation of a primary anti‐inflammatory activation phenotype. A combination of IL‐4/IL‐10/TGF‐β yielded a relatively stable and dominant immunosuppressive phenotype characterized by higher IL‐10 production and down‐regulated TNF‐α, IL‐6, CD86, CD274 and MHC II expression. Functionally, IL‐4/IL‐10/TGF‐β‐stimulated macrophages (M2) had a potent deactivating effect on a subsequent pro‐inflammatory LPS/IFNγ‐activated macrophage (M1) stimulation and significantly suppressed T‐cell proliferation. Monocytes derived from patients with chronic inflammatory diseases could be induced to be anti‐inflammatory using this protocol. Pre‐differentiation with GM‐CSF or M‐CSF was further demonstrated to enhance final M1/M2 activation status. Our findings indicate a robust polarization protocol for generation of specific immunosuppressive human monocyte‐derived macrophages.