THE IMMUNE SYSTEM EXPLAINED
The immune system is wonderful system of cells and signaling cytokines that fight infections and keep us healthy. We come in contact with billions of microorganisms every day. These include bacteria, viruses, fungi, and parasites. To protect us, we have an immune system. The immune system is a fascinating collection of infection fighting white blood cells and their partners the complement system and cytokines.
The complement system contains small proteins which circulate throughout the blood system. Their job is to recognize foreign substances (antigens), bind to them, and then activate the rest of the system. They stick to the bad cells and mark them so that the other immune cells can recognize the infectious cells. Another role of the complement system is to kill bacteria.
The next group is phagocytes. These cells can eat bacteria a process called phagocytosis. The phagocytes include granulocytes, macrophages which are converted monocytes, and dendritic cells. This system of cells is the first line of defense against infections.
Lymphocytes make up the next set. There are different types of lymphocytes and each has a specific function. T-helper cells are the main regulators of the immune system. When they come in contact with an antigen presenting cell such as a macrophage that has just eaten a bacteria, the helper cell is activated and it then helps turn on the rest of the immune system. Another type of T-cell is a killer T-cell. These cells circulate in the body looking for infections or infected normal cells, or even cancer cells. Their job is quite simple, when they find a bad cell, they kill it. B-lymphocytes help the immune system kill bacteria by producing immunoglobulins. Immunoglobulins act as tags that mark bacteria for removal by the phagocytes. These are produced every time you get and infection or an immunization. When the same bug invades your body, the B-lymphocytes remember and then produce more immunoglobulins via the plasma cells to help kill the infection.
Finally, there are substances called cytokines. These substances are used for a variety of purposes. They help the cells signal to each other, they can act as growth factors, they recruit immune cells, they activate immune cells, they turn off immune cells, and some even act as hormones. The cytokines are very important to keep the system running and they need to be in a balance. There are cytokines to turn on the system and to turn off the system. When there is an imbalance, the end result is either an immune deficiency or an overactive immune system. The overactive immune system is what is involved in chronic inflammation and this is a bad thing because of the diseases chronic inflammation causes. In fact, chronic inflammation has been implicated in heart disease, stroke, dementia, and cancer.