A) type I
B) type II
C) type III
D) type IV
Correct Answer: A
Solution :
When an adaptive immune response occurs in an exaggerated or inappropriate form causing tissue damage the term hypersensitivity is applied. Coombs and Gell (1963) have described four types of hypersensitivity reaction which are : Hypersensitivity?Type I Type I, or immediate hypersensitivity occurs when an IgE response is directed against innocuous antigens, such as pollen and the resuming release of pharmacological mediators (such as histamine) by IgE -sensitized mast cells produces an acute inflammatory reaction with symptoms such as astham or rhinitis. Thus, type I hypersensitivity is characterised by allergic reactions immediately following contact with antigen (allergen). The immediate anaphylactic response to bee venom is a clearcut example of type I hypersensitivity, due to the release of pharmacological mediators, including histamine, from mast cells. The reaction can produce generalized anaphylaxis and even death since the allergen is injected into the patient rather than being inhaled. Hypersensitivity - Type II Type II, or antibody-dependent cytotoxic hypersensitivity, occurs when antibody (IgG) binds to antigen on cells leading to phagocytosis, killer cell activity, or complement-mediated lysis. The mechanisms by which phagocytes damage cells in type II hypersensitivity reactions reflect their normal physiological functions in dealing with infectious pathogens. Hypersensitivity - Type III Type III, or immune complex mediated hypersensitivity develops when complexes are formed inlarge quantities, or cannot be cleared adequately by the reticuloendothelial system, leading to serum sickness type reactions. Eerual diseases result from immune complex formation may affect kidney, skin, lungs etc. Hypersensitivity - Type IV Type IV, or delayed type hypersensitivity (DTH) is manifested when antigen, for example tubercle bacilli, trapped in a macrophage. cannot be cleared. T lymphocyets are the stimulated to elaborate lymphokines which induce inflammatory reactions and activate and attract macrophages which release mediators. Other aspects of DTH reaction are seen in graft rejection and allergic contact dermatitis.
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