Hypersensitivity reactions

Hypersensitivity Reactions

Hypersensitivity reactions (pronunciation: hi-per-sen-si-tiv-ity re-ak-shuns) are a set of immune responses that are exaggerated or inappropriate against an antigen or allergen. These reactions are classified into four types: Type I, II, III, and IV, based on the Coomb's and Gell classification system.

Etymology

The term 'hypersensitivity' is derived from the Greek word 'hyper' meaning 'over' and the Latin word 'sensitivus' meaning 'feeling'. The term 'reaction' is derived from the Latin word 'reactio' meaning 'a response'.

Types of Hypersensitivity Reactions

Type I Hypersensitivity

Also known as immediate or anaphylactic reactions, Type I Hypersensitivity reactions are mediated by IgE antibodies. Common examples include allergic asthma, hay fever, and anaphylaxis.

Type II Hypersensitivity

Type II Hypersensitivity reactions are antibody-mediated and involve IgG and IgM antibodies directed against cell surface antigens, leading to cell damage. Examples include hemolytic anemia and Goodpasture's syndrome.

Type III Hypersensitivity

Type III Hypersensitivity reactions are immune complex-mediated. They occur when antigens and antibodies form complexes that deposit in tissues, causing inflammation and damage. Examples include serum sickness and Arthus reaction.

Type IV Hypersensitivity

Type IV Hypersensitivity reactions are T-cell mediated and do not involve antibodies. Examples include contact dermatitis and tuberculosis.

Related Terms

• Allergy
• Immunology
• Antigen
• Antibody
• Inflammation

External links

• Medical encyclopedia article on Hypersensitivity reactions
• Wikipedia's article - Hypersensitivity reactions

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