The Immune System - What is it and Its Connection With Allergic Reactions

This is the body's protective system and it works like a highly trained army fighting off invaders, such as bacteria and viruses, and foreign bodies, such as a splinter or insect sting. This army is made up of different cells, each with its own job to do.
The body's first line of defense includes the skin, tonsils, the hair in your nose and mucus in your nostrils and lungs. Stomach acid destroys the most harmful microorganisms. Enzymes in saliva and tears also kill bacteria.
If an invader does manage to make it past these defenses, however, the ground troops go to war. These are divided into white blood cells, or B cells, which are made in the bone marrow, and T cells, also made in the bone marrow, which may mature in the lymph glands.
B cells produce chemicals called antibodies or immunoglobulin. There are five types of antibody; one group plays an important part in allergies. They lock on to the surface of foreign substances, or antigens, such as bacteria and so help destroy them. Once the invading cells have been covered in antibodies they are easy prey for the T cells, which move in for the kill.
Usually this system works well, protecting us from the most diseases. But it relies on the B cells correctly recognizing an invader and going to work. Sometimes it works when we would rather it did not, by attacking a transplanted organ that it sees as foreign, for example.
The immune system is programmed to remember invaders and will muster its forces at the slightest hint of threat. This has helped scientists and doctors who regularly trick the immune systems into repelling viruses and bacteria, such as smallpox, by alerting them with a trace of a similar illness, cowpox.
When an allergen triggers the immune system's defenses, the body releases histamine, causing the classic allergy symptoms of swollen, watery and itchy nose, eyes and sinuses