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Immediate-Type Reaction – Causes, Symptoms & Treatment

An immediate-type reaction is an allergic response that occurs within minutes of exposure to an allergen. Mediated by immunoglobulin E (IgE), it can range from mild skin symptoms to life-threatening anaphylactic shock.

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Things worth knowing about "Immediate-Type Reaction"

An immediate-type reaction is an allergic response that occurs within minutes of exposure to an allergen. Mediated by immunoglobulin E (IgE), it can range from mild skin symptoms to life-threatening anaphylactic shock.

What Is an Immediate-Type Reaction?

An immediate-type reaction (also called a Type I hypersensitivity reaction or IgE-mediated allergy) is the fastest form of allergic response. It typically occurs within seconds to a few minutes after contact with an allergen and is triggered by the immune system. The immediate-type reaction is one of the four classical allergy types defined by Coombs and Gell and is the most commonly encountered type in clinical practice.

Causes and Mechanism

The trigger for an immediate-type reaction is an allergen – a substance that is harmless to most people but causes an exaggerated immune response in sensitized individuals. Common allergens include:

Pollen (e.g., grasses, trees, weeds)
Animal dander and epithelial particles
House dust mites
Foods (e.g., peanuts, milk, eggs, shellfish)
Insect venoms (e.g., bee or wasp stings)
Medications (e.g., penicillin, aspirin)
Latex

Mechanism of Action

During the first exposure to an allergen (sensitization phase), the immune system produces specific immunoglobulin E (IgE) antibodies. These IgE antibodies bind to mast cells and basophilic granulocytes in tissues and blood. Upon re-exposure to the same allergen, crosslinking of IgE antibodies on the cell surface triggers degranulation of mast cells: inflammatory mediators such as histamine, prostaglandins, leukotrienes, and tryptase are released. These mediators cause vasodilation, increased vascular permeability, smooth muscle contraction, and mucus secretion – the hallmark symptoms of an allergic reaction.

Symptoms

Symptoms of an immediate-type reaction vary depending on severity and the organ system affected:

Skin: Redness, itching, hives (urticaria), angioedema (swelling of deeper tissue layers)
Eyes and nose: Watery, red eyes (allergic conjunctivitis), sneezing, runny nose (allergic rhinitis)
Respiratory tract: Bronchospasm, wheezing, shortness of breath (up to allergic asthma)
Gastrointestinal tract: Nausea, vomiting, abdominal cramps, diarrhea
Cardiovascular system: Drop in blood pressure, rapid heartbeat, dizziness
Anaphylaxis: In the most severe cases, a life-threatening anaphylactic shock with circulatory failure and loss of consciousness can occur.

Severity Grades

Immediate-type allergic reactions are classified into four severity grades:

Grade I: Local skin reactions (redness, itching, urticaria)
Grade II: Mild systemic reactions (e.g., rhinitis, generalized urticaria, nausea)
Grade III: Severe systemic reactions (e.g., bronchospasm, vomiting, drop in blood pressure)
Grade IV: Anaphylactic shock with respiratory and circulatory arrest

Diagnosis

Several methods are available to diagnose an immediate-type reaction:

Medical history: Detailed interview about triggers, timing, and nature of symptoms
Skin prick test: Standardized skin test in which allergen solutions are applied to the skin and lightly scratched; wheal formation indicates sensitization
Intradermal test: Allergen is injected into the skin; more sensitive than the prick test
Specific IgE blood test (RAST/ImmunoCAP): Detection of allergen-specific IgE antibodies in the blood
Provocation test: Controlled exposure to the suspected allergen under medical supervision

Treatment

Acute Treatment

Acute treatment of an immediate-type reaction depends on the severity:

Antihistamines: Block the effects of histamine and relieve itching, redness, and mild swelling
Corticosteroids: Suppress the inflammatory response with a delayed onset; used in moderate to severe reactions
Bronchodilators: Open the airways in cases of bronchospasm (e.g., salbutamol inhaler)
Adrenaline (epinephrine): The treatment of choice for anaphylactic shock; administered intramuscularly, it causes immediate vasoconstriction, bronchodilation, and cardiac stimulation. People with known severe allergies often carry an adrenaline auto-injector (e.g., EpiPen).

Long-Term Treatment and Prevention

Allergen avoidance: Consistent avoidance of the triggering allergen
Specific immunotherapy (desensitization): Gradual increase of allergen doses to train the immune system for long-term tolerance, reducing sensitivity permanently
Anti-IgE therapy: Biologics such as omalizumab bind free IgE and can control severe allergic conditions

References

Coombs R.R.A., Gell P.G.H. - Classification of Allergic Reactions Responsible for Clinical Hypersensitivity and Disease. In: Gell P.G.H., Coombs R.R.A. (eds.), Clinical Aspects of Immunology, 3rd ed. (1975)
Ring J., Beyer K., Biedermann T. et al. - Guideline for acute therapy and management of anaphylaxis. Allergo J Int. 2014; 23(3): 96-112. DOI: 10.1007/s40629-014-0009-1
European Academy of Allergy and Clinical Immunology (EAACI) - EAACI Position Paper on Allergy Diagnosis and Management (2020). Available at: https://www.eaaci.org

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