人的机体就象一个小小的国家,必须有自我防护机制,以维护自身的安全,为此需要有一个自我防护系统,就象一个国家对外的边防和对内的警察。这两种全然不同的功能必须由免疫系统来加以完成,其细胞成分中的白细胞具有很大的活动性,经常不断地在身体的各个部位游走:有时见于机体的“外界面”,例如皮肤、肠道、呼吸道等;有时又可见于机体的各种内环境, Human beings, like a small country, must have a self-protection mechanism to safeguard their own security. To do this, a self-protection system is needed, like a nation’s external frontier and internal police. These two totally different functions must be completed by the immune system, the cellular components of the white blood cells with great activity, often constantly walking in various parts of the body: sometimes seen in the body’s “outer surface”, such as skin , Gut, respiratory tract, etc .; sometimes seen in the body’s various internal environment,