Immune system: what happens in the body during an allergy?

The immune system is what doctors call our body's defense system, which consists of organs, cells and proteins. The body's defenses are a very complex masterpiece of nature, because a multitude of functions and processes interlock here to keep the organism healthy and protect it from pathogens such as viruses, bacteria, fungi and parasites. Even scientists are constantly discovering new connections and have by no means explored all the mechanisms of the immune system, in which countless cells and proteins are involved.

Simply explained, the immune system consists of two parts: the innate, non-specific defense and the acquired, specific defense. Both perform different tasks that together form a hard-to-beat protective system against pathogens:

• Inherited immune defense: From birth, we are equipped with basic protection. About 90 percent of the defense work is done by the nonspecific defense, which includes the mucous membranes, the skin, defense cells and special proteins. It reacts in principle to all pathogens the same.
• acquired immune defense: For the fine work, the specific defense with its specialized leukocytes (divided into granulocytes, monocytes and lymphocytes) comes into play. For it is only after birth that the immune system continues to build up and learns with each contact with pathogens. For each pathogen - whether virus, bacterium, fungus or parasite - an individual defense mechanism is formed, which will be activated again in the future when contact is made again.

The immune system becomes active as soon as a pathogen encounters the body's first defense barrier. Our body has various external barriers that an unwanted intruder must first overcome. These include skin, mucous membranes, cilia, tears, saliva and stomach acid. Tear flow, increased formation of nasal secretions and sneezing are the first defensive reactions of the immune system to prevent a pathogen from entering the organism in the first place.

If an intruder has succeeded in breaking through the physical protective barrier on the skin or mucous membranes, the leukocytes go into action. For this, various immune cells come into play:

• The B lymphocytes, also called B cells, are responsible for the humoral immune response by producing antibodies in fluids such as blood, lymph and tissue fluids.
• Another important component of the immune system are the T lymphocytes or also called T cells, special white blood cells that are formed in the bone marrow. They are responsible for the cellular immune response by recognizing diseased cells and rendering them harmless. In addition, they take over the communication between messengers and cells.

Furthermore, messengers such as interleukins (IL) or interferons (IF) are part of a healthy immune system. Histamine is one of these messengers, which is released from mast cells during an allergic reaction [https://www.polli-allergie.de/symptome/ allergic-reaction/].

Antibodies, also called immunoglobulins (Ig), are proteins produced by B lymphocytes in immune response to pathogens to render the invaders harmless. They recognize specific features of the invader (antigens), store this information, and recall it when contact occurs again.

Antibodies are divided into five classes that perform specific tasks in different parts of the body:

• IgM
• IgG
• IgA
• IgD
• IgE

IgE antibodies are often involved in allergic reactions, and IgG antibodies can provide an indication of food allergy.

In an allergy there is a malfunction of the immune system. This is because it recognizes completely harmless substances as pests and fights them as such. So it can be that pollen, animal hair or dust mites are wrongly classified as an enemy, although they come in peace and mean the body no harm. Why that is with some humans in such a way, could not be clarified so far clearly. What is certain, however, is that a certain predisposition and various risk factors can favor the occurrence of an allergy.

On first contact with an allergen, sensitization takes place, which still proceeds without symptoms. The immune system then forms antibodies against the substance classified as malignant. It is not until the second contact with this substance that defense mechanisms such as rhinitis, eye itching and sneezing are set in motion. The harmless substance has now become the allergy trigger.

These allergens are proteins that lead to the release of histamine. This process makes itself felt through itching, sneezing, redness of the skin and swelling of the mucous membranes. Or, in other words, by, for example, allergic rhinitis or skin rash, as known to allergy sufferers.

Allergies are divided into different types. According to daab (German Allergy and Asthma Association), about 90 percent of allergy sufferers suffer from an immediate-type allergy in which the symptoms form immediately after contact with the allergen. Immediate-type allergies include, for example. hay fever, animal hair allergy, house dust allergy, insect sting allergy and food allergy.  They can be detected in the blood by IgE antibodies.

In contrast, contact allergy is a late-type allergy, as symptoms may not appear until days after contact with the allergen.