The Immune SystemThe immune system is made up of processes and structures within an organism that help protect it from foreign attackers. The immune system is made up of cells, tissues and organs; such as lymphocytes, lymph nodes, phagocytes and many others. For the immune system to function properly, it must first learn to distinguish between self and foreign cells. Cells marked “self” should be left alone. Foreign cells must be identified as “non-self” and trigger the immune system to begin defending the body. Any foreign microbe or antigen, an antigen is any substance that causes an immune response, will activate the immune system. To prevent autoimmune disease, a disease in which the body attacks its own cells, the cells must first undergo central tolerance; the ability of the immune system to recognize self-cells and not attack them. There are two types: first, central tolerance and second, peripheral tolerance. Central tolerance is acquired when the cell first grows in the bone marrow; the immature immune cell must learn not to attack its own body cells. If the ...