Microglia: gatekeepers of central nervous system immunology

Abstract

Microglia are perhaps the most underestimated cell type of our immune system. Not only were immunologists unaware of their capabilities until recently, but also, some neuroscientists denied their actual existence until the late 20th century. Nowadays, their presence is confirmed extensively, as demonstrated by numerous reports describing their involvement in virtually all neuropathologies. However, despite distinct approaches, their origin remains a point of controversy. Although many agree about their myeloid-monocytic ancestry, the precise progenitor cells and the differentiation mechanisms, which give rise to microglia in the different developmental stages of the CNS, are not unraveled yet. Mostly, this can be attributed to their versatile phenotype. Indeed, microglia show a high morphological plasticity, which is related to their functional state. This review about microglia aims to introduce the reader extensively into their ontogeny, cell biology, and involvement in different neuropathologies.

Microglia and Monocyte-Derived Macrophages in Stroke

“…Although many studies have found that microglia and monocytes/macrophages contribute to brain inflammation and injury in stroke, both cell types have overlapping functions and the ability to polarize toward pro-(M1) or antiinflammatory (M2) phenotypes. As such, their expression of common antigens and the morphological similarity between them have resulted in equivocal findings on their roles in stroke [9,[32][33][34]. The unique temporal and spatial presence of microglia and macrophages in the context of stroke suggest distinctive and complementary roles of each cell type in response to stroke injury.…”

P2X₇ receptor in the hippocampus is involved in gp120-induced cognitive dysfunction

“…Brain microglia, astrocytes, and innate immune cells of the brain parenchyma are responsible for homeostasis in normal CNS tissue, and are likely affected by ADC as excessive activation of microglial cells can induce CNS injury and neurodegenerative disease (Tambuyzer et al, 2009;Harry 2013;Hornik et al, 2014;Mosher and Wyss-Coray 2014). The P2X 7 receptor plays a major role in the regulation of microglia activity and is involved in inflammation and immune responses, and as such has an important role in neurodegenerative disease (Le Feuvre et al, 2002;Baudelet et al, 2015).…”

Genetic architecture, epigenetic influence and environment exposure in the pathogenesis of Autism

“…They can secrete TNF-α and IL-6 under inflammatory conditions, provide growth factors in early synaptogenesis, eliminate redundant synapses, and modulate synaptic transmission [78,79]. Morgan et al found microglial cells were activated in approximately 40% of their autism samples together with an increase in the average microglial somal volume in white mater [77].…”