Figu. 2

A schematic of a synapse showing pre, post elements, astrocytes and microglia. Brain and immune cells undergo a dynamic dialog. Peripheral immune cells, such as T-lymphocytes, macrophages and dendritic cells, coming from the cerebrospinal fluid or carried by blood vessels penetrate the brain through the blood brain barrier. They either have a surveilling activity or are attracted by the chemokines released by injured tissues. Microglia, the brain resident immune cells, perform a constant surveilling activity and are in particular attracted by synapse activity, locus of an intense interplay between neurons and glial cells. Many neurotransmitters circulate between these cell types resulting in the modulation of the synaptic functions. Increasing evidence suggest that molecules and signaling pathways first discovered for the immune system takes an important place in the physiological functioning of the synapse. Growth factor receptor (GF-R); Glutamate (Glu); Gamma Amino Butyric Acid (GABA); Acetylcholine (Ach); Dopamine (DA), Serotonin (5-HT), Adenosine tri-phosphate (ATP). (top scheme, cerebral structure inspired from [37])