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Updated: May 21, 2026
Assessment of Antibody-based Drugs Effects on Murine Bone Marrow and Peritoneal Macrophage Activation
Published on: December 26, 2017
TGFβ signaling plays a critical role in promoting alternative macrophage activation
Dapeng Gong1, Wei Shi, Sun-ju Yi
1Division of Hematology/Oncology, Children's Hospital Los Angeles, 4650 Sunset Boulevard, Los Angeles, CA 90027, USA.
Background:
Upon stimulation with different cytokines, macrophages can undergo classical or alternative activation to become M1 or M2 macrophages. Alternatively activated (or M2) macrophages are defined by their expression of specific gene products and play an important role in containing inflammation, removing apoptotic cells and repairing tissue damage. Whereas it is well-established that IL-4 can drive alternative activation, if lack of TGFβ signaling at physiological levels affects M2 polarization has not been addressed.
Results:
Vav1-Cre x TβRIIfx/fx mice, lacking TβRII function in hematopoietic cells, exhibited uncontrolled pulmonary inflammation and developed a lethal autoimmune syndrome at young age. This was accompanied by significantly increased numbers of splenic neutrophils and T cells as well as elevated hepatic macrophage infiltration and bone marrow monocyte counts. TβRII-/- CD4+ and CD8+ T-cells in the lymph nodes and spleen expressed increased cell surface CD44, and CD69 was also higher on CD4+ lymph node T-cells. Loss of TβRII in bone marrow-derived macrophages (BMDMs) did not affect the ability of these cells to perform efferocytosis. However, these cells were defective in basal and IL-4-induced arg1 mRNA and Arginase-1 protein production. Moreover, the transcription of genes that are typically upregulated in M2-polarized macrophages, such as ym1, mcr2 and mgl2, was also decreased in peritoneal macrophages and IL-4-stimulated TβRII-/- BMDMs. We found that cell surface and mRNA expression of Galectin-3, which also regulates M2 macrophage polarization, was lower in TβRII-/- BMDMs. Very interestingly, the impaired ability of these null mutant BMDMs to differentiate into IL-4 polarized macrophages was Stat6- and Smad3-independent, but correlated with reduced levels of phospho-Akt and β-catenin.
Conclusions:
Our results establish a novel biological role for TGFβ signaling in controlling expression of genes characteristic for alternatively activated macrophages. We speculate that lack of TβRII signaling reduces the anti-inflammatory M2 phenotype of macrophages because of reduced expression of these products. This would cause defects in the ability of the M2 macrophages to negatively regulate other immune cells such as T-cells in the lung, possibly explaining the systemic inflammation observed in Vav1-Cre x TβRIIfx/fx mice.
Insights
Transforming growth factor-beta (TGFβ) signaling is crucial for M2 macrophage polarization. Loss of TGFβ receptor II (TβRII) impairs M2 gene expression, leading to uncontrolled inflammation and autoimmune disease in mice.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages differentiate into M1 or M2 phenotypes upon cytokine stimulation.
- M2 macrophages are key in resolving inflammation and tissue repair.
- The role of TGFβ signaling in M2 polarization at physiological levels is unclear.
Purpose of the Study:
- To investigate the impact of TGFβ signaling deficiency on M2 macrophage polarization.
- To elucidate the molecular mechanisms underlying TGFβ's role in M2 macrophage function.
Main Methods:
- Utilized Vav1-Cre x TβRIIfx/fx mice with hematopoietic-specific TβRII deletion.
- Analyzed immune cell populations, including macrophages, neutrophils, and T cells.
- Assessed M2 macrophage markers (e.g., Arginase-1, Ym1) in bone marrow-derived macrophages (BMDMs) and peritoneal macrophages.
- Examined signaling pathways including Stat6, Smad3, Akt, and β-catenin.
Main Results:
- Mice lacking TβRII in hematopoietic cells developed severe pulmonary inflammation and autoimmune syndrome.
- TβRII-deficient BMDMs showed impaired basal and IL-4-induced production of M2-associated genes (Arg1, Ym1, Mgl2).
- Loss of TβRII reduced Galectin-3 expression in BMDMs.
- Impaired M2 polarization was independent of Stat6 and Smad3 but correlated with reduced phospho-Akt and β-catenin.
Conclusions:
- TGFβ signaling is essential for regulating genes characteristic of alternatively activated (M2) macrophages.
- Reduced TβRII signaling diminishes the anti-inflammatory M2 phenotype.
- This defect may contribute to immune dysregulation and systemic inflammation observed in the mouse model.
