Mesenchymal Stem Cells Convert Human Macrophages to a Novel Type of Alternatively Activated Macrophages.

Abstract 3632

Poster Board III-568

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 anti-inflammatory/immune modulatory effects. All studies were approved by IRB of University of Wisconsin School of Medicine and Public Health. MSCs were culture expanded from discarded bone marrow filters after bone marrow harvest from normal healthy sibling HLA-matched donors. We used passages -35 for our experiments. Ex vivo culture expanded MSCs were characterized by their cell surface phenotype (positive for MSC markers: CD29, CD44, CD73, CD90, and CD105; and negative for hematopoietic markers: CD31, CD34, and CD45), and their differentiation potential into bone, fat and cartilage. Monocytes were isolated from peripheral blood mononuclear cell fraction of healthy donors using CD14+ Miltenyi magnetic bead cell separation method. We cultured human CD14+ monocytes for seven days without any added cytokines to generate macrophages, and then co-cultured them for three 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 co-culture period, and phagocytic assays to investigate their functional activity in vitro. Macrophages co-cultured with MSCs consistently showed high level expression of CD206, a marker of alternatively activated macrophages, in addition to being positive fro CD14 marker. Using CD1a and CD209 staining we did not detect presence of any dendritic cells either at the end of seven days culture of monocyte-derived macrophages or at the end of co-culture period. Furthermore, macrophages that were co-cultured with MSCs expressed high levels of IL-10 and low levels of IL-12, as determined by intracellular staining, typical of alternatively activated macrophages. However, macrophages co-cultured with MSCs also expressed high levels of IL-6 and low levels of TNF-α, compared to controls. Functionally, macrophages co-cultured with MSCs showed a higher level of phagocytic activity using Alexa 488-conjugated E. coli phagocytic assay. In summary we describe a novel type of human macrophage generated in vitro after co-culture with MSCs that assume 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 macrophages with potentially significant role in tissue repair.