How the Immune System Responds to Allergies

An allergy is the result of an overreaction by the body's immune system in the presence of an allergen. However, how does that work, exactly? Knowing how the immune system responds to allergies will help you to  understand what is happening when you suffer that runny nose, itchy rash or stomach upset.

Immune System Allergic Response

An allergy is actually a category of hypersensitivity. Substances, also called allergens or antigens, which most people would suffer no problem with, cause other folks immune system to go into overdrive. Here is what is happening 'under the hood'...

How the Immune System Works

Immune System Diagram - Image Credit: National Institute of Allergy and Infectious Diseases
Immune System Diagram

There is a system in the body that runs parallel to the blood vessels, called the lymph system. It plays a major role in keeping disease and infections at bay. Much of that is concentrated in the lymph nodes, part of the system that produces lymphocytes, cells that attack disease.

Tonsils, the appendix and others are also lymphoid tissue. However, there is so-called lymphoid tissue elsewhere, including most importantly the bone marrow and the thymus which is an organ just behind the breastbone. The thymus produces T cells, which are a type of white blood cell. These T cells play a key role in allergies.

Because of many articles written on AIDS over the years, the name of these cells is widely recognized. However, what do they do?

They have several functions, but one of the primary ones is to patrol the blood and lymphatic fluid looking for foreign substances. Every cell in our bodies has a genetic 'signature' that is unique to us. Anything, like a bacteria or virus, that has a different signature is seen as a foreign substance and a candidate for removal.

Some T cells merely mark those foreigners as foreign, and then phagocytes or other mechanisms remove the substances. Some T cells communicate with B cells to help them do their job in the immune system. In addition, some T cells directly attack those foreign proteins.

Mast cells (a type of white blood cell) in conjunction with basophiles (another type) rush to the site of such an invader. On cue, they cause biochemical’s such as histamines and prostaglandins to flood the area. That helps engulf the invader, neutralizing it. The package is then carried away and out of the body.

Overactive Immune System and Allergies

But that reaction can go too far. If an otherwise harmless substance gets marked for destruction, the whole process is carried out unnecessarily. If the reaction is larger than needed, too much histamine and other substances can be released.

In either case, the result is an allergic reaction.

The runny nose from a nasal inflammation (allergic rhinitis), red and watery eyes from inflamed eyelid membranes (conjunctivitis), red skin welts (urticaria skin hives) or other common allergy symptoms all follow from those processes. The body is overreacting, causing the immune system to go into hyper drive and cause harm to itself.

Building up the immune system is one major key to good health. However, like anything, balance is essential. Too weak a reaction would leave us vulnerable to disease while too strong a reaction creates an allergy.