Abstract
Over the past twenty years, numerous studies have shown that the immune system makes a real contribution to the construction and functioning of the brain, as well as to the development of neurological and psychiatric pathologies. This is the case, for example, in the progression of neurodegenerative diseases, notably Alzheimer's disease. On the one hand, this contribution involves the action of immune cells outside the brain, and of secreted factors which can directly modulate neuronal activity. On the other hand, studies have highlighted the central role played by microglia in the assembly of circuits, the regulation of synaptic transmission, and the formation or elimination of synapses during the different phases of life: development, learning and neurodegeneration. A growing number of studies show that microglia are involved in almost all neurological and psychiatric diseases. Through their sensitivity to systemic signals such as inflammation, or to the microbial environment, or to that of the microbiota, microglia thus constitute a veritable interface between the bodily environment and brain circuits in physiological and pathological contexts.
Until the turn of the century, immunologists and neurobiologists worked in parallel in the construction of knowledge. Today, in view of the challenges of integrating these new data into the exploration of brain and nervous system function, and of the link to be made between studies of normal physiology and those focused on pathologies, it seems essential to develop a systemic approach that integrates all the players present, including immune cells, and to consider the brain in its dynamic construction and evolution. The aim is to establish a new neuro-glio-immune schema for the development, physiology and pathology of brain circuits. Characterizing these neuro-immune interactions is a source of hope - but also of fantasy - for the development of new therapeutic approaches targeting different types of pathology. That's why it's vital to put scientific facts back at the heart of the discussion: we need to clearly define the stakes involved in this rapprochement, and specify what has been established in animal models but has yet to be explored in humans, in order to support the progression of knowledge and understanding in a rational way.
