Explain the Process of IgE-Mediated Allergic Response?

Basically, there are three steps involved with the IgE-mediated allergic response

These include:

Step 1: Sensitization

Step 2: Early phase reaction

Step 3: Late phase reaction

Let us understand this process.

The body's immune system normally reacts to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight these invaders. However, sometimes the immune system reacts to ordinarily benign substances such as food or pollen, to which it has become sensitive. Sensitization therefore is the first step in the IgE- mediated allergic response. If our immune system is inclined to form IgE to certain foods, our body must be exposed to the food before we can have an allergic reaction. In other words, people with food allergies have an unusually sensitive immune system. A true food allergy occurs when the body's immune system reacts to a protein from a particular food that has been swallowed. This protein is called an allergen.

The allergen causes the persons own antibodies to attack the foreign substance. Thus initial exposure to allergen leads to production of allergen-specific IgE. Production of allergen-specific IgE starts a chain reaction of chemical changes, which cause adverse reactions in the body. Reaction may occur immediately, in a few minutes, or several hours after the food is eaten (i.e. within minutes of subsequent exposure of the IgE antibody to the allergen). This is the second phase of the allergic reaction called the early phase reaction. As the food is digested, it triggers certain cells in our body to produce a food-specific IgE in large amounts. The food-specific IgE is then released and gets attached to the surfaces of mast cells. The next time we eat that food, it interacts with food-specific IgE on the surface of the mast cells and triggers the cells to release chemicals such as histamine, which is a key mediator of the early allergic response, producing smooth muscle constriction, mucus secretion, vascular permeability and sensory nerve stimulation. To illustrate, if you are allergic to a particular food, you may first feel itching in the mouth as you start to eat the food. After the food is digested in the stomach, you may have gastro intestinal disturbances such as vomiting, diarrhoea, or pain.

When the food allergens enter and travel through the bloodstream, they may cause your blood pressure to drop, As the allergens reach the skin, they can cause hives or eczema. When the allergens reach the lungs, they may cause airway obstruction, asthma etc. Allergen also stimulates immune cells (e.g., mast cells, T-cells) to produce inflammatory mediators (e.g., leukotrienes, cytokines). The newly formed mediators act at post- capillary endothelial cells, promoting outflow of plasma leading to localized oederna, adhesion of circulating leukocytes, infiltration of tissues by eosinophils, neutrophils, and basophils. Over the course of several hours, the infiltrating inflammatory cells become activated and release mediators stimulating and enhancing further inflammatory reactions. This is the late phase reaction.