MS is largely confined to the central nervous system and the myelin in the peripheral nervous system is relatively untouched. This also occurs in most EAE models although in some there is some peripheral nerve involvement as occurs in the notably in the rabbit. The autoimmune disease of the CNS in animals is called experimental autoimmune encephalomyelitis (EAE) but in the peripheral nerve it is called experimental autoimmune neuritis (EAN). In Lewis rat EAE and EAN both result in hindlimb paralysis but in mice the clinical picture is different, in EAE there is paralysis but in EAN these is not paralysis but clenching of feet and altered gait. Although the myelin in peripheral nerve and the central nervous system share some proteins, there are differences between the two. This suggests that in MS the target is different to a demyelinating disease of the peripheral nervous system called Guillain Barre Syndrome. The immune system is very good at distinguishing between different targets and if you sensitize mice to peripheral (sciatic=leg nerve) nerve compared to spinal nerves the immune system targets into the relevant tissue although they may be next to each other.
In this slide from the spinal cord it shows the
peripheral nerves next to the spinal cord just before the peripheral
nerve enters the spinal cord. The round grey blobs are white blood cells
the red line is the junction between central and peripheral nerves.
This suggests the thing causing MS should be found in the CNS lesions and shows how exquisitly specific an autoimmune response can be as there are similar proteins that occur both in the central and peripheral nerves.
Central nerve myelin is made by oligodendrocytes and one cell makes myelin shealth for many nerves cells
Peripheral nerve myelin is more compact and is made by a schwan cells; one schwan cell per nerve