PECAM1 and hydrops fetalis: The other three categories of cells that resided in HF microenvironment included: (i) vascular cells such as endothelial cell (EC, Pecam1+) and smooth muscle cell (SM, Acta2+), (ii) fibroblast cell (FB, Pdgfra+), and (iii) various immune cells such as Macrophage 1 (Mac1, Cd68+), Macrophage 2 (Mac2, Cd163+), Langerhans cell (LC, Cd207+), and T cell (TC, Cd3g+) (Fig. 2B and 2C; Table S1).