S1PR1 and hydrops fetalis: In this study, we tested the role of S1PR1 expressed in macrophages in HF diet-induced atherosclerosis in Ldlr KO mice by first generating mice selectively lacking S1pr1 gene expression in myeloid cells, including macrophages, and then transplanting BM from these mice into recipient Ldlr KO mice to generate chimeras that lacked S1pr1 expression in BM-derived myeloid cells.