Stokes et al. (2013) provides a new intriguing glimpse into their neural infrastructure and dynamics. “
“The CNS is a complex organ, to say the least. Numerous cell types act in accord to maintain its integrity and its functions, separated into three PD173074 main groups: neurons, the glia, and endothelial cells. Previously thought to be outnumbered 10:1, new data estimate that neurons are present in equal proportion to glial cells across the CNS, although this ratio is highly variable, depending on

the region studied (Azevedo et al., 2009). A clear count of the number of endothelial cells across the CNS has not been reported, although it was shown that endothelial cells and neurons are present in similar amounts in the amygdaloid complex (García-Amado and Prensa, 2012). In

any case, neurons, glial cells, and endothelial cells exist in close proximity of each other, forming find more the neurovascular unit (NVU), a coherent view of the CNS as a whole instead of a blend of compartmentalized cell types (Zlokovic, 2008). When it comes to its defense, the CNS also has highly peculiar specificities. Devoid of a lymphatic system, its integrity is guarded exclusively through an innate immune system with an adaptive immunity only present in specific conditions (Rivest, 2009). The term “immune privilege” has often been used to describe the defenses of the CNS. While it is true that specific responses

are in place in this organ, the same can be said for every organ in the body. For instance, the lungs respond to a given insult in a specific way that might not be as efficient as in the spleen. In a way, every organ Dipeptidyl peptidase in the body is immune privileged. Such a term also suggests that immune processes are not as important in the CNS as in other organs. The innate immune system, however, is highly active in the CNS, organizing a complex response involving every cell type present. Another concept regarding the integrity of the CNS that needs to be tackled is that, in normal physiology, the blood-brain barrier (BBB) is a hermetic wall shielding the CNS from any outside contacts. However, the BBB is actually a tightly controlled membrane through which active transport is organized and plays a central role in the control of innate immune responses. We will strive in this Review to highlight the importance and frequency of immune responses in the CNS and also to show the need of seeing such responses as a continuous crosstalk between numerous cell types in the CNS and the periphery, not as a linear event. The CNS is not an island separated from the rest of the body but rather an integral member of it, in constant link with its environment. In humans, one-fifth of the body’s total energy consumption takes place in the CNS.