Hypersensitivity is triggered by the immune system's overreaction to typically harmless substances. These substances, known as antigens, can originate from within the body or the external environment. The immune system mistakenly identifies these antigens as threats, leading to an inflammatory response and various symptoms depending on the type and location of the reaction.
Types of Hypersensitivity and Their Causes
Several factors contribute to hypersensitivity, often categorized into types:
-
Type I (Immediate Hypersensitivity): This type involves IgE antibodies and mast cell degranulation, causing rapid reactions like allergies to pollen, food, or medications. The cause is exposure to a specific allergen. [Reference: Medical News Today – What are the different types of hypersensitivity reactions?]
-
Type II (Cytotoxic Hypersensitivity): This involves IgG or IgM antibodies binding to cell surface antigens, leading to cell destruction. Examples include some autoimmune diseases. The causes are complex and often involve genetic predisposition and environmental factors. [Reference: Merck Manual – Overview of Hypersensitivity and Reactive Skin Disorders]
-
Type III (Immune Complex Hypersensitivity): This involves the deposition of antigen-antibody complexes in tissues, causing inflammation. Examples include serum sickness. The cause is usually exposure to a foreign antigen. [Reference: Not directly stated in provided references, but implied by the definition of Type III hypersensitivity].
-
Type IV (Delayed-Type Hypersensitivity): This involves T-cell mediated responses, with delayed inflammation appearing hours or days after exposure to the antigen. Examples include contact dermatitis (e.g., poison ivy) and hypersensitivity pneumonitis (an allergic lung reaction). The cause is exposure to an antigen that triggers a cellular immune response. [References: NHLBI, NIH – Interstitial Lung Diseases - Hypersensitivity Pneumonitis; Cleveland Clinic – Hypersensitivity Pneumonitis: Causes, Symptoms & Treatment]
Specific Examples of Hypersensitivity Causes
- Drug Hypersensitivity: Reactions to medications, like vancomycin, demonstrate how drugs can act as antigens. [Reference: UpToDate - Vancomycin hypersensitivity]
- Visceral Hypersensitivity: This involves a lowered pain threshold in internal organs, often linked to functional gastrointestinal disorders. Causes are not fully understood but may involve nervous system dysregulation and inflammation. [Reference: Cleveland Clinic - Visceral Hypersensitivity: Symptoms, Treatment, Causes & What it Is]
- Hypersensitivity Pneumonitis: This lung condition is caused by inhaling certain organic dusts, like mold spores or bird droppings. [References: NHLBI, NIH – Interstitial Lung Diseases - Hypersensitivity Pneumonitis; Cleveland Clinic – Hypersensitivity Pneumonitis: Causes, Symptoms & Treatment]
- Oral Hypersensitivity: A wide range of substances, including food, additives, and medications, can cause oral hypersensitivity reactions. [Reference: MAAOM - Oral Hypersensitivity Reactions]
In summary, many types of particles and substances from the external environment or from within the body are recognized by the immune cells as antigens, triggering hypersensitivity reactions. The specific cause varies depending on the type of hypersensitivity.
