【網(wǎng)絡(luò)綜合 - 研究生考試(考研)試題】
The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune system in defending the body relies on a dynamic regulatory communications network consisting of millions of cells. Organized into sets and subsets, these cells pass information back and forth like clouds of bees swarming around a hive. The result is a sensitive system of checks and balances that produces an immune response that is prompt, appropriate, effective and self-limiting.

　　The heart of the immune system is the ability to distinguish between self and non-self. When immune defenders encounter cells or organisms carrying foreign of non-self molecules, the immune troops move quickly to eliminate the invaders. Virtually every body cell carries distinctive molecules that identify it as self. The body’s immune defenses do not normally attack tissues that carry a self marker. Rather, the immune cells and other body cells coexist peaceably in a state k