Type II hypersensitivity

Type II hypersensitivity

In type II hypersensitivity (or cytotoxic hypersensitivity)cite web |url=http://pathmicro.med.sc.edu/ghaffar/hyper00.htm |title=Hypersensitivity reactions |format= |work= |accessdate=] the antibodies produced by the immune response bind to antigens on the patient's own cell surfaces. The antigens recognized in this way may either be intrinsic ("self" antigen, innately part of the patient's cells) or extrinsic (absorbed onto the cells during exposure to some foreign antigen, possibly as part of infection with a pathogen). These cells are recognized by macrophages or dendritic cells which act as antigen presenting cells, this causes a B cell response where antibodies are produced against the foreign antigen.

An example here is the reaction to penicillin where the drug can bind to red blood cells causing them to be recognised as different, B cell proliferation will take place and antibodies to the drug are produced. IgG and IgM antibodies bind to these antigens to form complexes that activate the classical pathway of complement activation to eliminate cells presenting foreign antigens (which are usually, but not in this case, pathogens). That is, mediators of acute inflammation are generated at the site and membrane attack complexes cause cell lysis and death. The reaction takes hours to a day.

Another form of type 2 hypersensitivity is called antibody-dependent cell-mediated cytotoxicity (ADCC). Here, cells exhibiting the foreign antigen are tagged with antibodies (IgG or IgM). These tagged cells are then recognised by natural killer (NK) cells and macrophages (recognised via IgG bound (via the Fc region) to the effector cell surface receptor, CD16 (FcγRIII)), which in turn kill these tagged cells.

ome examples

*Autoimmune hemolytic anemia
*Goodpasture's syndrome
*Pemphigus
*Pernicious anemia (if autoimmune)
*Immune thrombocytopenia
*Transfusion reactions
*Graves disease
*Myasthenia gravis
*Rheumatic fever
*Hemolytic disease of the newborn (erythroblastosis fetalis)
*Acute transplant rejection

References


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