|MadSci Network: Immunology|
The blood-brain barrier refers to the inability of blood-derived chemicals to pass into the brain. The endothelium of the capillaries of the brain forms an inpermeable barrier to chemicals found in the blood. However, cells of the immune system can cross the barrier through a process called diapedesis or extravasation. The cells of the immune system can actively squeeze through the junctions between the endothelial cells to enter the tissue. In fact, it is probably the immune system that carries viruses and intracellular bacteria into the brain that causes some infections in the brain. Yes, in addition, the brain has its own immune components and scavenger cells. Some of these cells are called pericytes and microglial cells (specific to the brain). These cells are not specific to particular antigens, such as T and B cells, but are part of the non-specific immune response system.
Try the links in the MadSci Library for more information on Immunology.