Immune process in allergy
The immune system produces many classes of protective antibodies (namely IgM, IgG, IgA, IgD, IgE) to fight against bacterial, viral and parasitic infections. The IgE antibody is specially produced as a defense against helminth parasite infestation (for example Ascaris or round worms in the intestine). However in modern homes the risk for Ascaris infestation is minimal due to hygienic disposal of human waste via the flush system.

Allergy suffers have an imbalance in their immune mechanism that causes them to produce excessive amounts of IgE antibody following exposure to harmless inert allergens. It is not clear why these individuals produce high levels of IgE antibody to the harmless allergens but genetic factors have been implicated. The IgE antibody formed against the provoking allergen (e.g. egg, peanuts, dust mites and others) is continuously released into the tissues and also the blood system. The circulating IgE antibody has a natural tendency to bind to mast cells present in abundance in the skin and the mucosal tissues. The IgE antibody can also bind to other cells such as basophils and eosinophils. The person with IgE-bound mast cells is now considered to be sensitized to react to the specific allergens. When these sensitized individuals come across the same allergen again, the IgE antibody on mast cells reacts with the provoking allergen. This results in the de-granulation of the mast cells causing the release of histamine and other inflammatory mediators. Histamine is a major mediator in allergy and asthma. Histamine has a complex and multiple roles in the inflammatory responses. The degranulation of mast cells and basophils result in release of a variety of mediators including histamine. Histamine has many biological effects including dilating blood vessels, increasing vascular permeability, and stimulating certain nerve endings in immediate hypersensitivity reactions. Recent studies show that histamine released in inflammatory reactions may help recruit some types of immuno-competent cells (bearing histamine receptors) and affect their maturation, activation, polarization and effector functions in chronic inflammation. Histamine may also regulate Th1 and Th2 cells to a degree and therefore modulate the allergy response.

 

The released inflammatory mediators not only cause damage to the tissues but also attract other inflammation causing cells including basophils and eosinophils. The presence of potent chemical mediators released by many types of cells cause the development of allergic symptoms. The nature of the symptoms differs depending on the organ but the basic molecular mechanism is similar.

Therefore, at least two conditions are necessary for the development of IgE-mediated allergy. They are: (1) exquisite sensitivity to produce large amounts of IgE antibody to normally harmless organic substances (allergens). Such persons are usually genetically predisposed for allergy and usually there is a family history of allergy, (2) a recurrent or continuous exposure to the provoking allergen.

Thus, the measurement of total IgE level and allergen-specific IgE antibody in blood is the key to effective diagnosis and management of the allergy. Avoidance of the provoking allergen responsible for the allergy brings immediate relief to the allergy or asthma suffers.