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Updated: Dec 9, 2025
Polarization of M1 and M2 Human Monocyte-Derived Cells and Analysis with Flow Cytometry upon Mycobacterium tuberculosis Infection
Published on: September 18, 2020
The In Vitro M1/M2 Polarization of Macrophages of BCG-Infected Mice
D A Il'in1, V A Shkurupy2,3
1Research Institute of Experimental and Clinical Medicine, Federal Research Center of Fundamental and Translation Medicine, Novosibirsk, Russia. ilindenis.ilin@yandex.ru.
Abstract:
Cultured peritoneal macrophages from intact (control) and BCG-infected (experiment) male BALB/c mice were studied 90 days after infection. Polarization of macrophages by M1 (expression of GM-CSF, IFNγ, and CD16/32) and M2 (expression of bFGF and CD36) differentiation pathways was studied with consideration for their the nuclearity class. Mononuclear cells predominated (90% and higher) in macrophage cultures of both groups and presumably, were presented by mainly epithelioid cells. The results indicated polarization of mononuclear and multinuclear macrophages in the M2 direction under conditions of BCG granulomatosis and a higher initial M2 polarization of binuclear macrophages. In control cultures, the ratio of M2 to M1 macrophages was 0.57, in experimental cultures this ratio was 1.6. It seems that long persistence of Mycobacterium tuberculosis in macrophages served as a factor stimulating the plastic processes and transformation of macrophages into epithelioid cells that form the "core" of granulomas and their enlargement upon incorporation of macrophages.
Insights
BCG infection promotes M2 macrophage polarization in mice, transforming them into epithelioid cells. This suggests Mycobacterium tuberculosis persistence drives granuloma formation and expansion.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophages play a crucial role in the immune response to Mycobacterium tuberculosis (BCG).
- Macrophage polarization into M1 (pro-inflammatory) and M2 (anti-inflammatory/tissue repair) phenotypes influences disease outcome.
- Granuloma formation is a hallmark of tuberculosis, involving macrophage transformation.
Purpose of the Study:
- To investigate macrophage polarization in response to persistent BCG infection.
- To examine the role of macrophage nuclearity in M1/M2 differentiation.
- To understand the cellular mechanisms underlying granuloma formation.
Main Methods:
- Cultured peritoneal macrophages from BCG-infected and control mice were analyzed 90 days post-infection.
- Macrophage polarization was assessed by M1 markers (GM-CSF, IFNγ, CD16/32) and M2 markers (bFGF, CD36).
- Nuclearity of macrophages (mononuclear, binuclear, multinuclear) was considered in the analysis.
Main Results:
- Mononuclear cells, primarily epithelioid cells, predominated in both groups.
- BCG infection induced a significant shift towards M2 polarization in both mononuclear and multinuclear macrophages.
- The M2:M1 ratio increased from 0.57 in controls to 1.6 in BCG-infected cultures.
- Binuclear macrophages showed higher initial M2 polarization.
Conclusions:
- Persistent Mycobacterium tuberculosis infection drives macrophage polarization towards the M2 phenotype.
- Macrophage plasticity and transformation into epithelioid cells are stimulated by persistent mycobacterial infection.
- These transformed macrophages are key components of granulomas, contributing to their growth.
