Updated on November 7, 2024
What is Hypersensitivity?
Hypersensitivity, frequently referred to as an allergic reaction, is an overreaction of the immune system to a generally considered harmless substance.
This overreaction can lead to a range of symptoms, from mild discomfort to life-threatening conditions. The condition can manifest in various ways, affecting the skin, respiratory system, or entire body.
Types of Hypersensitivity
Hypersensitivity is broadly categorised into four types based on the mechanisms of immune response and the time it takes for the symptoms to appear: Type I, Type II, Type III, and Type IV.
Type I Hypersensitivity (Immediate Hypersensitivity)
Type I hypersensitivity is also known as immediate hypersensitivity because symptoms typically develop within minutes of exposure to the allergen. Immunoglobulin E (IgE) antibodies mediate this type.
- Examples include allergic rhinitis (hay fever), asthma, and anaphylaxis.
- Common Allergens: Pollen, dust mites, pet dander, insect stings, and certain foods like peanuts and shellfish.
Type II Hypersensitivity (Cytotoxic Hypersensitivity)
Type II hypersensitivity, also known as cytotoxic hypersensitivity, is mediated by Immunoglobulin G (IgG) and Immunoglobulin M (IgM) antibodies. This type of reaction occurs when certain antibodies attack the surface of cells, destroying them. Antibodies called IgG or IgM attach to antigens on the surface of target cells, marking them for immune cell destruction, potentially leading to autoimmune diseases.
- Examples: Conditions such as autoimmune hemolytic anaemia, transfusion reactions, drug-induced hemolytic anaemia, Goodpasture’s syndrome, and Rh incompatibility in newborns are examples of Type II hypersensitivity.
- Symptoms: Depending on the condition, symptoms can include fatigue, weakness, or more severe symptoms like kidney failure.
Type III Hypersensitivity (Immune Complex Hypersensitivity)
Type III hypersensitivity involves the formation of immune complexes, which are aggregates of antigens and antibodies. These complexes can deposit in various tissues, leading to inflammation and tissue damage. In Type III hypersensitivity, immune complexes form in the bloodstream and are deposited in multiple tissues, triggering an inflammatory response. This response can cause tissue damage and dysfunction.
Examples: Diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, and serum sickness are associated with Type III hypersensitivity.
Symptoms: Depending on where the immune complexes are deposited, symptoms can include joint pain, skin rashes, and organ dysfunction.
Type IV Hypersensitivity (Delayed-Type Hypersensitivity)
Type IV hypersensitivity, also known as delayed-type hypersensitivity, occurs several hours to days after exposure to the allergen. Unlike the other types, this hypersensitivity is mediated by T-cells rather than antibodies. In Type IV hypersensitivity, T-cells recognise antigens presented by antigen-presenting cells and release cytokines, leading to an inflammatory response. This process is slower and can take hours to days to develop.
- Examples: Conditions such as contact dermatitis (e.g., poison ivy rash), tuberculin skin test reactions, and chronic transplant rejection are examples of Type IV hypersensitivity.
- Symptoms: Symptoms can vary but typically include redness, swelling, and pain at the site of exposure.
Factors Contributing to Hypersensitivity
- Genetics: A family history of allergies or hypersensitivity disorders increases the risk.
- Environmental factors: Exposure to allergens, pollutants, and certain chemicals can trigger hypersensitivity.
- Immune system dysfunction: Underlying immune system problems can contribute to exaggerated responses.
- Age: Hypersensitivity can occur at any age but is often more prevalent in children and young adults.
Managing Hypersensitivity
Effective management of hypersensitivity involves avoiding known allergens, using medications to control symptoms, and, in some cases, undergoing immunotherapy.
- Avoidance: The first line of defence is to avoid exposure to known allergens. This may involve changing your environment, such as using air purifiers, avoiding certain foods, or taking precautions outdoors during high pollen seasons.
- Medications: Antihistamines, corticosteroids, and decongestants are commonly used to manage symptoms of hypersensitivity. For more severe cases, epinephrine may be prescribed for use in emergencies, such as during anaphylactic reactions.
- Immunotherapy: Immunotherapy, encompassing allergy shots or sublingual tablets, progressively desensitises the immune system to particular allergens. This approach significantly treats allergies related to pollen, dust mites, and insect stings.
Non-Allergic Hypersensitivity Reactions
While the term “hypersensitivity” is often synonymous with allergic reactions, you should know that there’s a difference between these and non-allergic hypersensitivity reactions.
Some people may experience severe, rapid-onset reactions to certain drugs or foods that mimic allergic reactions but do not involve the immune system. These responses are often called non-allergic drug hypersensitivity reactions or pseudoallergic, distinctive, or anaphylactoid reactions.
Crucially, unlike allergic reactions, these non-allergic hypersensitivity reactions do not involve the production of antibodies or the activation of T cells. Instead, they directly trigger symptoms without the intermediary involvement of the immune system.
This distinction is often challenging based on symptoms alone, necessitating careful medical evaluation to determine the underlying cause of the reaction.
Conclusion
Hypersensitivity is a complex condition that can significantly impact the lives of those affected. Understanding the different types of hypersensitivity and the factors contributing to its development is needed for effective prevention and management.
If you or anyone you know experience symptoms of hypersensitivity, it’s important to consult a healthcare professional for proper diagnosis and treatment. Additionally, recent developments in treatment can help better manage their symptoms and improve their quality of life.
Sources
- https://www.sciencedirect.com/topics/medicine-and-dentistry/hypersensitivity
- https://emedicine.medscape.com/article/136217-overview\
- https://www.msdmanuals.com/home/skin-disorders/hypersensitivity-and-reactive-skin-disorders/overview-of-hypersensitivity-and-reactive-skin-disorders
- https://www.healthdirect.gov.au/allergies-and-hypersensitivities
- https://dermnetnz.org/topics/allergies-explained
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