Human Embryonic Stem Cell-Derived and Fetal Macrophages Exhibit Mainly Features of Alternative (M2) Polarization.

Abstract 4598

Monocyte heterogeneity has long been recognized and 2 functional subsets of human monocytes that exert specific roles in homeostasis and inflammation in vivo, M1 and M2 monocytes, has been described. The different monocyte subsets seem to reflect developmental stages with distinct physiological roles but few is known whether the macrophage diversity arises in early ontogeny.

Human embryonic stem cells (hESC) provide an unique model for in vitro studies of the early ontogeny of the hematopoietic system. Human embryonic monocytes were obtained from embryoid bodies cultured for 3 weeks in the presence of BMP4, VEGF and a mixture of hematopoietic cytokines. The sorted CD14⁺CD45⁺ cells were further cultured for 7 -10 days in the presence of GM- and M-CSF. Embryonic stem cells derived monocytes and macrophages were identified by several criteria including morphology, cytochemical staining, ultrastructural and functional features. In contrast to early mouse hematopoiesis that bypass the series of monoblaste/monocyte precursors human embryonic monocyte lineage developped by process similar to definitive monopoiesis. Two distinct subpopulations of monocytes, first CD14⁺CD16^- then CD14⁺CD16⁺ could be successively identified. Transcriptional and functional assays suggest that CD14⁺CD16^- population is not an embryonic counterpart of CD14⁺CD16^- “inflammatory” adult monocytes but a precursor for CD14⁺CD16⁺ macrophages and dendritic cells. Moreover, both tested populations possess phenotypical markers of M2 polarization and were positive for a expression of scavenger receptors CD163⁺ and CD36⁺ of CCR5 and negative for CD62L. Additional transcriptional studies and chemokine pattern confirmed their IL10 ^high IL12^low phenotype, clearly indicating their M2 polarization state. M2 polarization was confirmed in fetal macrophages derived from CD34⁺ cells issued from livers of first-trimester fetuses. Involvment of embryonic and foetal monocytes in homeostasis are under investigation.

Collectively, our data provide insight into alternative macrophage polarization during early embryogenesis and adds further data to the growing body of evidence that establishment of macrophage heterogeneity is related to early ontogeny.