Macrophages (meaning “big eaters”) are actually monocytes from the blood stream that have been “turned on” by interacting with lymphocytes, which themselves have been turned on by other macrophages that have encountered a foreign protein. These cells have an amazing appetite and ability to damage tissue. For example, in tuberculosis, macrophages cause the tissue damage to lungs and other tissues.
In MS, macrophages appear to be the primary cause of myelin damage. Using an electron microscope, you can see actual chunks of myelin inside macrophages in plaques.
A drawing of a plaque by Charcot using a simple microscope. Char-cot described the illustration as “Patch of sclerosis in the fresh state. Lymph-atic sheath of a vessel distended by voluminous fatty globules.” The fat-laden cells are surrounding a tiny blood vessel in an MS plaque and the cells are filled with myelin. These cells are actually macrophages that have damaged myelin, resulting in “demyelination.”
Another drawing by Charcot showing loss of normal myelin around a small blood vessel. This blood vessel is a venule with five or six long, bean-like nuclei oriented more or less vertically in the middle of the drawing. Also seen are spaghetti-like axons without myelin, which appear smaller than the other axons with their myelin intact. This observation led to multiple sclero-sis being termed a “demyelinating disease.”