Hematopoiesis: a Brief Overview

Hematopoiesis represents the continuous process of formation of all the blood cells, that occurs throughout life, starting from the hematopoietic stem cells (HSCs). Multiple studies have proved that this process is structured in two stages, the primitive wave and the definitive one, resulting in the production of all blood cell types: erythrocytes, neutrophils, eosinophils, basophils, monocytes, lymphocytes and platelets. The objective of this Review is to present the general aspects of this process for a better understanding, including the molecules that influence lineage-specific differentiation, hematopoiesis being one of the most important elements in maintaining one’s body homeostasis. This Review describes hematopoiesis, from the beginning, starting with HSCs, throughout fetal development and adult life, including the niches of formation and maturation of hematopoietic stem cells and the factors that influence all the proliferation and differentiation processes. The niches of formation represent local microenvironments of bone marrow tissue which participate in the maintenance, functioning and quiescence of hematopoietic stem cells. The factors that control all the processes of proliferation and differentiation are represented by transcription factors, physical cell-cell interactions and cytokines; they are either produced locally, in the bone marrow, or they can be transported to this, through the blood, being produced elsewhere. The study of hematopoiesis, stem cell plasticity and control mechanisms, offers the opening for interesting approaches for the investigation and treatment of various malignant, inflammatory, and degenerative pathological processes.