Phagocyte Development

AbstractMature circulating white blood cells can be divided into two lineages: lymphoid and myeloid. The lymphoid lineage consists of T, B, NK and innate lymphoid cells, while the myeloid lineage includes functionally and morphologically distinct cell types including mononuclear phagocytes (monocytes, dendritic cells and macrophages), granulocytes (neutrophils, basophils, mast cells and eosinophils) and platelets. Granulocytes and mononuclear phagocytes are key players at all stages of the immune response from its genesis to its resolution, and come under the banner of phagocytes. Damaged or infected tissue releases chemoattractants that rapidly recruit these phagocytes to the site of injury. Once at the inflamed site, these cells coordinate and carry out immune functions, playing a key role in host defence. The recent past has seen major progress in our understanding of phagocyte developmental biology. Here, we discuss the latest advances in myeloid development, underpinning our current understanding of how these cells are generated and maintained.Key ConceptsThe myeloid lineage includes functionally and morphologically distinct cell types including mononuclear phagocytes (monocytes, dendritic cells and macrophages) and granulocytes (neutrophils, basophils, mast cells and eosinophils).The majority of tissue resident macrophages are generated before birth and are long‐lived self‐maintained cells throughout adulthood.Dendritic cells prime naïve T cells and are derived from a common precursor in the bone marrow that gives rise exclusively to this family of cells.Monocytes are the principal circulating mononuclear phagocyte. Monocytes develop in the bone marrow from a common monocyte progenitor, once in the circulation classical monocytes have the potential to convert into nonclassical monocytes. Classical monocytes are known to repopulate resident mononuclear phagocyte populations and have potent effector functions during immunity.Granulocyte subsets have a complex morphology with a segmented nucleus and each subset contains granules endowing them with a specific role in host defence.Transcription and growth factors control and dictate the development of phagocytes.