Elsevier

Experimental Hematology

Volume 37, Issue 12, December 2009, Pages 1445-1453
Experimental Hematology

Immunobiology
Mesenchymal stem cell–educated macrophages: A novel type of alternatively activated macrophages

https://doi.org/10.1016/j.exphem.2009.09.004Get rights and content

Objective

Mesenchymal stem cells (MSCs) are capable of modulating the immune system through interaction with a wide range of immune cells. This study investigates the hypothesis that interaction of MSCs with macrophages could play a significant role in their antiinflammatory/immune modulatory effects.

Materials and Methods

MSCs were derived from bone marrow and monocytes were isolated from peripheral blood of healthy donors. We cultured human monocytes for 7 days without any added cytokines to generate macrophages, and then cocultured them for 3 more days with culture-expanded MSCs. We used cell surface antigen expression and intracellular cytokine expression patterns to study the immunophenotype of macrophages at the end of this coculture period, and phagocytic assays to investigate their functional activity in vitro.

Results

Macrophages cocultured with MSCs consistently showed high-level expression of CD206, a marker of alternatively activated macrophages. Furthermore, these macrophages expressed high levels of interleukin (IL)-10 and low levels of IL-12, as determined by intracellular staining, typical of alternatively activated macrophages. However, macrophages cocultured with MSCs also expressed high levels of IL-6 and low levels of tumor necrosis factor–alpha (TNF-α) compared to controls. Functionally, macrophages cocultured with MSCs showed a higher level of phagocytic activity.

Conclusions

We describe a novel type of human macrophage generated in vitro after coculture with MSCs that assumes an immunophenotype defined as IL-10–high, IL-12–low, IL-6–high, and TNF-α–low secreting cells. These MSC-educated macrophages may be a unique and novel type of alternatively activated macrophage with a potentially significant role in tissue repair.

Section snippets

Cell culture

We used human blood and bone marrow to derive monocytes and MSCs, respectively. All protocols were approved by the Health Sciences Institutional Review Board of University of Wisconsin-Madison School of Medicine and Public Health. Monocytes were isolated from human peripheral blood by using magnetic bead separation methods according to manufacturers' protocols. Briefly, peripheral blood mononuclear cells were collected from the blood of healthy donors by density gradient separation using

Isolation and characterization of MSCs from human BM

All MSCs derived from normal healthy BM were positive for MSC markers (CD29, CD44, CD73, CD90, CD105) and negative for hematopoietic markers (CD31, CD34, CD45, CD54) (data not shown), as described previously [22]. Specifically, MSCs expressed high levels of CD90 and were negative for CD14 cell surface marker, while macrophages expressed an opposite pattern. MSCs derived from BM could differentiate into bone, fat, and cartilage in vitro, using appropriate growth factors (data not shown).

MSCs increase expression of CD206 on cocultured macrophages

To test

Discussion

Macrophages are widely distributed in many different tissues in the human body and are a key component of innate immunity. These cells differentiate from circulating peripheral blood monocytes after migration into tissues, either to replace long-lived tissue macrophages or in response to injurious insults [33]. Macrophages, in addition to their role in initial phases of tissue defense, play an indispensable role in later phases of tissue homeostasis and repair, such as removal of cellular

Acknowledgments

This work was supported by National Institutes of Health/National Heart, Lung and Blood Institute (Bethesda, MD, USA) HL081076 K08 grant (to P.H.) and also by funding from University of Wisconsin Carbone Cancer Center (Madison, WI, USA). The authors gratefully thank Dr. Laura Hogan for the critical reading of the manuscript.

Conflict of Interest Disclosure

No financial interest/relationships with financial interest relating to the topic of this article have been declared.

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