HES1 is required for mouse fetal hematopoiesis.

Background: Hematopoiesis in mammal is a complex and highly regulated process in which hematopoietic stem cells (HSCs) give rise to all types of differentiated blood cells. Previous studies have shown that hairy and enhancer of split (HES) repressors are essential regulators of adult HSC development downstream of Notch signaling.

Methods: In this study, we investigated the role of HES1, a member of HES family, in fetal hematopoiesis using an embryonic hematopoietic specific Hes1 conditional knockout mouse model by using phenotypic flow cytometry, histopathology analysis, and functional in vitro colony forming unit (CFU) assay and in vivo bone marrow transplant (BMT) assay.

Positive feedback between PGE2 and COX2 redirects the differentiation of human dendritic cells toward stable myeloid-derived suppressor cells.

Dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) show opposing roles in the immune system. In the present study, we report that the establishment of a positive feedback loop between prostaglandin E(2) (PGE(2)) and cyclooxygenase 2 (COX2), the key regulator of PGE(2) synthesis, represents the determining factor in redirecting the development of CD1a(+) DCs to CD14(+)CD33(+)CD34(+) monocytic MDSCs. Exogenous PGE(2) and such diverse COX2 activators as lipopolysaccharide, IL-1β, and IFNγ all induce monocyte expression of COX2, blocking their differentiation into CD1a(+) DCs and inducing endogenous PGE(2), IDO1, IL-4Rα, NOS2, and IL-10, typical MDSC-associated suppressive factors.