[Microglia: immune cells sculpting and controlling neuronal synapses]

The development of new animal models and functional analysis methods has dramatically changed our understanding of the physiology of microglial cells. These cells which are the resident macrophages of central nervous system have the ability to adapt rapidly to subtle changes of their environment. Recent findings indicate in particular that they can establish contacts with neuronal synapses that they can eliminate and modulate by releasing specific mediators. Here we review the experimental observations that have revealed the occurrence of these interactions not only in pathological conditions but also in the healthy brain and in particular during normal brain development. The discovery of bi-directional communications between synapses and microglia sheds a new light on our understanding of brain functioning and should allow a better understanding of brain functioning and of interactions between immune and nervous systems.