Macrophages in Hematopoiesis and Related Blood Diseases

Emerging evidence indicates that macrophages play important roles in hematopoiesis in addition to their immune functions. The well-known immune-unrelated functions of macrophages include their roles in hematopoiesis, especially the quality control of hematopoietic stem cells (HSCs) and hematopoietic stem and progenitor cells (HSPCs), the support of erythropoiesis, and the regulation of megakaryopoiesis. Several studies, most using mouse models, have explored the roles of macrophages in hematopoiesis in different organs such as the yolk sac (YS), fetal liver (FL), bone marrow (BM), and spleen (SP). We have recently documented the potential roles and underlying mechanisms of macrophages in myeloproliferative neoplasm (MPN), aplastic anemia (AA), and idiopathic thrombocytopenic purpura (ITP). In this article, we review the origin of macrophages, introduce their roles in regulating HSCs/HSPCs, erythropoiesis, and megakaryopoiesis within four hematopoietic organs, and summarize the recent advances of macrophages in MPN, AA, and ITP. Finally, we outline the unresolved questions that future studies should address to explore in greater depth the role of macrophages in both normal and disordered hematopoiesis.