Cerebrospinal fluid (CSF) is a fluid that surrounds the central nervous system (CNS). The workings of the CSF is not clearly understood but it is clear that it fulfills several important functions:
Whereas most of the immune system cells (leukocytes) in the blood are of a type called granulocytes, CSF usually contains other types of leukocyte called lymphocytes and monocytes. The presence of antibodies, secreted by some of the lymphocytes, indicates some kind of inflammation. Such inflammation is typical both of multiple sclerosis and some other diseases. Additionally, people with MS usually have specific lymphocyte cells, called B-cells, which are directed against the proteins that make up myelin, the insulating material around the nerve cells (neurons). These proteins are myelin basic protein (MBP), proteolipid protein and myelin oligodendrocyte protein. Myelin, itself, is often found in the CSF of people with MS. These findings, as well as other abnormalities in the CSF, are the basis of the use of spinal taps for diagnosing MS.
Cerebrospinal fluid is isolated both from the brain and the blood by a protective layer called the ependyma or Blood-Brain-Barrier (BBB). This barrier shields the CNS from both toxins and from invading bacteria and viruses (pathogens). However mechanisms within the BBB involving adhesion molecules, cytokines and pore proteins regulate the movement of leukocytes and other traffic to and from the CSF.
Cerebrospinal fluid links:
Cerebal Ventricular System and Cerebrospinal Fluid
Cerebrospinal fluid circulation -- Medical Illustration
Figure 14: Cerebrospinal Fluid
Cerebrospinal Fluid Cytokines