The Mincle ligand trehalose dibehenate differentially modulates M1‐like and M2‐like macrophage phenotype and function via Syk signaling

Introduction Macrophages play a significant role in the progression of diseases, such as cancer, making them a target for immune‐modulating agents. Trehalose dibehenate (TDB) is known to activate M1‐like macrophages via Mincle, however, the effect of TDB on M2‐like macrophages, which are found in the tumor microenvironment, has not been studied. Methods qRT‐PCR, flow cytometry, cytokine ELISA, and Western Blotting were used to study the effect of TDB on GM‐CSF and M‐CSF/IL‐4 derived bone marrow macrophages (BMMs) from C57BL/6 and Mincle−/− mice. Results TDB treatment up‐regulated M1 markers over M2 markers by GM‐CSF BMMs, whereas M‐CSF/IL‐4 BMMs down‐regulated marker gene expression overall. TDB treatment resulted in Mincle‐independent down‐regulation of CD11b, CD115, and CD206 expression by GM‐CSF macrophages and CD115 in M‐CSF/IL‐4 macrophages. GM‐CSF BMMs produced of significant levels of proinflammatory cytokines (IL‐1β, IL‐6, TNF‐α), which was Mincle‐dependent and further enhanced by LPS priming. M‐CSF BMMs produced little or no cytokines in response to TDB regardless of LPS priming. Western blot analysis confirmed that the absence of cytokine production was associated with a lack of activation of the Syk kinase pathway. Conclusion This study illustrates that TDB has the potential to differentially regulate M1‐ and M2‐like macrophages in the tumor environment. Trehalose dibehenate (TDB), a known vaccine adjuvant, has been shown to induce the activation of M1‐like macrophages, however, not much is known about its effect on M2‐like polarized macrophages found in the tumor microenvironment. Here, we determine that TDB increases the pro‐inflammatory response of M1‐like macrophages and skews the M2‐like macrophage to a more neutral phenotype.