It is necessary for the immune system to clearly distinguish foreign cells and proteins from those made by the body.

(a) Explain why this is the case:

It is necessary for the immune system to clearly distinguish foreign cells and proteins from those made by the body so that the immune system will be able to fight foreign cells and proteins and eliminate them from the body.

Explanation: The ability of the immune system to clearly distinguish foreign cells and proteins from those made by the body helps the body to identify pathogens that invade the body and trigger appropriate immune response to eliminate the foreign cells and proteins.

When the immune system of the body fails to distinguish foreign cells and proteins from those made by the body, the body launches an attack against its cells, that is the immune system triggers an autoimmune response in which attacks are launched against the cells of the body and destroy them. This condition in which the immune system recognizes the cells of the body as non-self and launches an attack against them is known as autoimmunity. Autoimmunity is the major cause of most degenerative diseases such as type I diabetes mellitus.

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