Microglia are not brain macrophages?

Microglia are commonly referred to as the brain`s macrophages, which leads to confusion due to the presence of several other macrophage populations in the central nervous system. The morphological, molecular and ontological differences between these cells are subtle. They need to be clearly defined in the light of the new evidence suggesting that microglia originate not in the bone marrow, but from yolk sac, or, possibly, pericyte progenitors. Recent paradigm shift redefines the specific roles of microglia during brain development, health and disease. Microglia have emerged as key players in important events such as neurogenesis, programmed cell death, elimination of synapses and remodeling of neural circuits. These novel discoveries imply a need for a better morphological and molecular differentiation of mononuclear phagocyte populations and their subtypes in the brain. This may improve our knowledge of their specific contributions and possible pharmacological manipulation in brain health and disease.