Hypersensitivity reaction: why immunity sometimes becomes dangerous

I felt worse after the injection, is it an allergy?

Immunity is designed to protect the body — that’s its mission. But what to do when this defense system loses control? When the whole body swells after insect bites, when medications cause shock, and pollen or a piece of nut triggers an «alarm siren» throughout the body? Or when your own cells become a target?

This is how it manifests itself hypersensitivity reaction — a condition in which the immune system responds too strongly, too quickly, or... to something she shouldn't respond to at all. This is the basis of many allergies, autoimmune diseases, reactions to drugs or vaccines. But this process has a clear structure and types - and you need to know about them in order to recognize and stop the risk in time.

What is a hypersensitivity reaction?

A hypersensitivity reaction is inadequate immune response to the antigen that causes tissue damage or excessive inflammation. This reaction occurs even to harmless substances - pollen, milk protein, medications, your own cells. It is based on - excessive activation of immune cells, the production of antibodies or cytokines that trigger the inflammatory cascade.

Why does it occur?

• Dysregulation of the immune response — congenital or acquired.

• Genetic predisposition — for example, to atopic reactions.

• Trigger factors — infections, toxins, stress, hormonal changes.

• Contact with new antigens — medicines, proteins of foreign origin.

Types of hypersensitivity according to the Gell & Coombs classification

Type I: immediate reaction (allergic)

• Mechanism: IgE antibodies attach to mast cells and basophils. Upon re-exposure to the allergen, the cells release histamine.

• Symptoms: itching, edema, rash, rhinitis, bronchospasm, anaphylaxis.

• Time of occurrence: from a few seconds to 30 minutes.

Type II: cytotoxic hypersensitivity

• Mechanism: IgG or IgM antibodies attack self cells.

• Consequences: complement activation, cell destruction, inflammation.

• Examples: hemolytic disease of the newborn, reaction to blood transfusion.

Type III: immune complex

• Mechanism: immune complexes deposit in blood vessels, kidneys, and joints.

• Manifestations: fever, rash, vasculitis, kidney damage, arthralgia.

• Examples: systemic lupus erythematosus, serum sickness.

Type IV: delayed (T-cell)

• Mechanism: activation of CD4+ and CD8+ T-lymphocytes → release of interleukins → chronic inflammation.

• Onset of symptoms: 24–72 hours after contact.

• Examples: contact dermatitis (latex, cosmetics), Mantoux reaction, transplant rejection.

Hypersensitivity to medications is a special category

Drug reactions can be of any of four types. The most common are:

• Allergy to antibiotics (type I)

• Penicillin-induced hemolysis (type II)

• Rash or vasculitis after immunomodulators (type III)

• Stevens–Johnson syndrome (type IV)

Dangerous reactions — anaphylaxis, exfoliative dermatitis, nephritis — require emergency care.

How to determine the type of reaction?

Tests that may be prescribed:

• Total IgE, specific IgE (type I)

• Immunogram (cellular and humoral indicators)

• Antibodies to cellular structures (ANA, anti-DNA, anti-erythrocyte)

• Skin or kidney biopsy (type III/IV)

• Skin tests (prick test, patch test)

• Drug challenge tests — only in a clinic setting!

Treatment: depending on the type, but with one principle - reduce immune aggression

• Antihistamines (type I)

• Systemic corticosteroids (all types in severe cases)

• Immunosuppressive therapy (type II and III, less often IV)

• Allergen-specific immunotherapy (ASIT) — for type I allergy

• Trigger avoidance — the basis of prevention

• Monitoring of immune parameters — control of the inflammatory process

Hypersensitivity is not just about allergies. It about systemic immune failures, which can appear suddenly, or develop over years. A proper understanding of the types and mechanisms allows not only to alleviate symptoms, but also to prevent serious complications. If the body's reaction seems excessive, consult an allergist or immunologist. Because sometimes the immune system can really "overdo it.".