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Hematopoiesis is the process by which blood cells are formed. It has been a broadly studied system since the second half of the 20th century. Attention was drawn to this process after the discovery, in 1951, of the protective role that bone marrow intravenous infusion had against radiation. In the mid-1950s, it was subsequently discovered that this protection was caused by transplanted stem cells contained in the bone marrow. Multipotency of the hematopoietic stem cells (HSCs) was further proven during the 1960s, with the development of clonal in vivo repopulation assays. Following clonal in vitro assays, together with the study of cell surface markers and flow sorting, have configured the current view of the hematopoietic system, as a tree-like hierarchy with the HSCs at the top and mature cells at the bottom (Figure 1.1) [1, 2]. Hematopoiesis is active throughout life and it maintains the pool of mature blood cells, which constitute one of the human tissues with highest turnover. Broadly speaking, specialized blood cells can carry out four main functions: 1) The innate immune system, composed, among others, by macrophages, dendritic cells and granulocytes, constitutes the first defense against infection 2) The adaptive immune system, composed by B and T lymphocytes, carries out a delayed and specialized response against pathogens. 3) Red blood cells transport oxygen to every cell 4) Platelets take care of wound healing. |
