How Does Backup Immune System Begin to Work?

Intrinsic Immune System is a systemic and harmonious body defense system and it plays fatal role in keeping human body in a healthy condition. Normally, people will get sick if the following two conditions occur: one is the amount of external harmful factors is more excessive than the eliminating ability of body intrinsic immune system and the other one is the immunity become lower even though the external harmful factors still stay in the same level.
No matter which condition occurs, intrinsic immune system will become abnormal, leading to disease appearance. Well then, what reaction will the body make in such condition? The most scientific one is that human body will activate the backup immune system as soon as the intrinsic immune system becomes abnormal. The first method is to activate the complement system to work together with intrinsic immune system. Complement System is always in a rest condition and it only begins to work when intrinsic immune system has abnormality. Therefore, we always think complement system is a kind of non-mainstream defense system, which is also the reason we call is alternative pathway of activating complement. This complement system also have a strong immunity once it is activated, cooperating with intrinsic immune system closely. The second method is to start the activation system of antigen presenting cell (APC). APC is a group of cells with high stimulation ability. APC can stimulate and activate the adaptive immune system through some specific method and the activation of this system is a kind of natural reaction of human body after intrinsic immune system disorder. The main acting method is to offer related information of disorder cells to adaptive immune system, activating T cell and B cell to work.
Actually, the above can also be described simply as the following sentences. When intrinsic immune system finds it is not enough to defense the harmful factors, it will release some immune stimulating factors to activate C3 which can play immunity of complement. On the other hand, intrinsic system will stimulate the APC, which provides abnormal cell antigen to adaptive immune system and then adaptive system can recognize them.
We call the above two activation procedure as immune response. Once immune response is started, all backup immune system enters into the immune reaction period. They work together with intrinsic cells to defense the disease. All the harmful factors will be eliminated after a period of cooperative work of intrinsic immune system can backup immune system, which also refers to the body condition from sick to health. We call this ability of self-returning health as the healing power of nature.
When human body returns to healthy condition, backup immune system begins to rest again and intrinsic immune system also begin to normal work independently gradually. This recovery ability we call it human body immune limit ability. Normal immune limit ability is important to help human body get rid of sick condition.