THE IMMUNE SYSTEM IS A NETWORK OF CELLS AND ORGANS that defends the body against attacks by foreign invaders. The cells communicate with each other through proteins called cytokines to mount a defensive attack. The body is mainly being defended against what are popularly called germs or microbes (bacteria,yeast, protozoan, and viruses). Because the mammalian body provides an ideal environment (warmth and moisture) for many microbes, they tend to multiply easily and rapidly in the body if the immune system has been unable to keep them out or destroy them. symptoms or illness may arise directly from the actions of the pathological organisms, from the immune system activities called upon to fight them, and /or both. The immune systems is amazingly complex. Every time we solve a problem, two more question arise. The immune system must recognize dozens of different enemies and then produce secretions and "killer" cells to match up with and wipe out each one of them. But it gets even trickier: the immune system must produce this response only when the enemy is present; otherwise, the immune system would be draining energy and building up secretions continuously.