How do the white blood cells get into the brain and spinal cord

When lymphocytes become turned on by an immune reaction, they, in turn, "turn on" or "activate" blood monocytes. Once activated, monocytes become macrophages and develop incredible appetites. The activated lymphocytes and macrophages have "Velcro-like" molecules on them called adhesion molecules. When these cells stick to the inside of the tiniest blood vessels that have corresponding adhesion molecules, they then become able to eat their way through the vessel into the nervous system (Figure 6).

Central Nervous System

Central Nervous System

myelinated axon

T lymphocyte GDC

myelinated axon

Blood/Brain Barrier

Blood

T lymphocyte GDC

perivascular inflammation . • .

Tysabri

Figure 6. Immunopathogenesis of MS. Mechanisms of demyelination are shown diagrammatically in this illustration. Cells (lymphocytes and macrophages) cross the blood-brain barrier and enter the brain and spinal cord (the central nervous system). These cells then damage myelin. Myelin antibody may also play some role in demyelination. MBP is a major protein component of myelin; Tysabri stops these cells from attaching to the cerebral endothelium and crossing. Note the tight junctions of the endothelium,

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