Healthy immune system
The immune system is so complex that some of the way it works is not yet understood. What scientists do know is that a healthy immune system battles infectious agents in an effort to keep the body free of disease. When a disease-producing organism invades the body the white blood cells (called leukocytes) form a kind of army that gathers together to prevent infection. Leukocytes also work to repair any damage done by an invader.
Just as there are a variety of foreign materials that act as invaders (viruses, bacteria, parasites, and fungi), there are many types of white blood cells. Different ones have different functions. One type, called neutrophils, ingests bacterial invaders and produces the chemicals that destroy them. Whatever the type, white blood cells work together to help produce the body’s immune response.
The immune system protects the body from harmful substances. The immunity response (inflammation) is part of innate immunity. It occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause.
White blood cells are assisted by lymphocytes — cells that play the most prominent role in helping the body create a natural resistance to disease. There are two types of lymphocytes: B cells and T cells. B lymphocytes produce antibodies that do battle with antigens, the foreign substances that are created by an invader. When an invader enters the body, its antigens alert the immune system to the invader’s presence.
When antibodies target the invader, they also send messages to white blood cells to join the battle. T lymphocytes attack cells that are foreign or that are infected by a virus. They do this by generating antibodies that fight off the foreign particles found in invading cells. Their attack also includes digesting the invaders or releasing chemicals that can destroy them. Another job of the T cells is to help the body accept — without overreacting to — the chemicals that are found in allergy shots.
Among the substances that the immune system encounters are allergens, which can trigger allergic reactions in many people. Some of the most common allergens are pollen, mold, and animal dander, as well as cockroach and house dust mite droppings. Scientists do not know why some substances are allergens for some people and harmless for others.
The body has two main ways of protecting itself. Innate immunity is the body’s first line of defense. It includes the barriers that keep antigens from entering your body, such as the skin, mucus, stomach acid, the cough reflex, and enzymes in tears and skin oils. An antigen that gets past these barriers then has to face other parts of the immune system, such as certain white blood cells that “eat” microorganisms and dead or damaged cells. Inflammation, or swelling, is also part of innate immunity. Blood vessels leak fluid into damaged tissues. This swelling keeps foreign substances away from other body tissues.
Active (acquired) immunity is slightly different, occurring when the body responds to a foreign invader such as a virus. In active immunity, the body responds to an antigen and builds a defense that is specific to that antigen. In other words, the first time the body comes in contact with a foreign invader, it creates antibodies that attack only that invader. The next time the same antigen enters the body, the immune system is already prepared to fight it. In a sense, the immune system “remembers” the antigen.
When a body has a healthy immune system, some invaders can be conquered before they create the condition that leads to disease. The damage from other invaders that succeed at first can be minimized and repaired. When an immune system is not healthy, it is not able to work as well in fighting off these invaders. In some cases, an immune system becomes so compromised that it shuts down and is unable to fight off or contain any disease-producing organisms.
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