Abstract 10226: M2 Macrophages Contribute to Postnatal Lymphangiogenesis as Lymphatic Endothelial Cell Progenitors
Introduction: Macrophages possess two characteristics, pro-inflammatory and anti-inflammatory ones. Respective macrophages are called M1 and M2 type. M2 macrophages have been shown to predict a poor prognosis due to accelerating lymph node metastasis in patients with cancer. Recently, macrophages have been shown to contribute to lymphangiogenesis in various pathological states. We have reported that implantation of adipose-derived regenerative cells (ADRCs) augment lymphangiogenesis. We now assessed our hypothesis that M2 macrophage served as the lymphatic endothelial cell (LEC) progenitors and promoted lymphangiogenesis in edematous tissues.
Methods: Macrophages were isolated from the peritoneal cavity of C57BL/6J mice by induction of aseptic peritonitis. We cultivated those either in RPMI (control medium) or EGM-2MV that contains growth factors suitable for LECs. Immunocytochemistry was performed to detect CD11b. We also analyzed LYVE-1 as a LEC marker and CD163 as a M2 macrophage-specific marker. Finally we examined the role of macrophages in lymphangiogenesis using a mouse tail lymphedema model. Tail diameter was measured to assess the extent of lymphedema. Histological examination was performed to detect new lymphatic vessels or macrophages.
Results: More than 90% of the freshly isolated macrophages were positive for CD11b, however CD163 positive cells were only 10%. All macrophages were negative for LYVE-1. Cells examined at 14 days of culture in EGM-2MV were positive for both CD163 and LYVE-1. In vivo, lymphedema was significantly improved by implantation of ADRCs. The ratio of the number of LYVE-1 positive LECs divide by total macrophages was greater in ADRC group compared to the control group (0.72±0.05 vs 0.06±0.03 ;p<0.01). LECs were almost all positive for CD163. A greater number of LYVE-1+/CD163+ M2 macrophages, a higher lymphatic capillary density (p<0.000005), and less inflammatory cell infiltration (p<0.001) were observed in the ADRC group compared to the control group.
Conclusions: Macrophages accumulating at the edematous tissues seemed to polarize to M2 type and might contribute to lymphangiogenesis as LEC progenitors.
- © 2011 by American Heart Association, Inc.