Type II hypersensitivity, in the Gell and Coombs classification of allergic reactions, is an antibody mediated process in which

IgG Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG ...

and

IgM Immunoglobulin M (IgM) is one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. IgM is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antig ...

antibodies are directed against antigens on cells (such as circulating red blood cells) or extracellular material (such as basement membrane). This subsequently leads to

cell lysis Lysis ( ) is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ''lysate''. In molecular bio ...

, tissue damage or loss of function through mechanisms such as # complement activation via the

classical complement pathway The classical complement pathway is one of three pathways which activate the complement system, which is part of the immune system. The classical complement pathway is initiated by antigen-antibody complexes with the antibody isotypes IgG and IgM ...

Antibody-dependent cellular cytotoxicity Antibody-dependent cellular cytotoxicity (ADCC), also referred to as antibody-dependent cell-mediated cytotoxicity, is a mechanism of cell-mediated immune defense whereby an effector cell of the immune system actively lyses a target cell, whose ...

or # anti-receptor activity. The activation of the complement system results in

opsonization Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound. Thus, opsonins act as tags to label things in the body that should be phagocytosed (i.e. ...

, the

agglutination In linguistics, agglutination is a morphological process in which words are formed by stringing together morphemes, each of which corresponds to a single syntactic feature. Languages that use agglutination widely are called agglutinative lang ...

of red blood cells, cell lysis, and cell death. These reactions usually take between 2 and 24 hours to develop.

Examples

An example of complement dependent type II hypersensitivity is an

acute hemolytic transfusion reaction An acute hemolytic transfusion reaction (AHTR), also called immediate hemolytic transfusion reaction, is a life-threatening reaction to receiving a blood transfusion. AHTRs occur within 24 hours of the transfusion and can be triggered by a few milli ...

following transfusion of

ABO The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. For human blood transfusions, it is the most important of the 43 different blood type (or group) classification system ...

incompatible blood. Preformed antibody (predominantly IgM) against donor red cell antigens not found in an individual of a particular blood group (e.g. anti-A IgM in an individual with blood group B), bind to the donor red cell surface and lead to rapid complement mediated haemolysis and potentially life-threatening clinical consequences. Complement-dependent type II hypersensitivity can also occur during the transmission of incompatible maternal antibodies to fetal red blood cells causing hemolytic anemia in the fetus, known as erythroblastosis fetalis. Another example of a complement dependent type II hypersensitivity reaction is

Goodpasture's syndrome Goodpasture syndrome (GPS), also known as anti–glomerular basement membrane disease, is a rare autoimmune disease in which antibodies attack the basement membrane in lungs and kidneys, leading to bleeding from the lungs, glomerulonephritis, ...

, where the basement membrane (containing collagen type IV) in the lung and kidney is attacked by one's own antibodies in a complement mediated fashion. An example of anti-receptor type II hypersensitivity (also classified as type V hypersensitivity) is observed in

Graves disease Graves' disease (german: Morbus Basedow), also known as toxic diffuse goiter, is an autoimmune disease that affects the thyroid. It frequently results in and is the most common cause of hyperthyroidism. It also often results in an enlarged thyro ...

, in which anti-thyroid stimulating hormone receptor antibodies lead to increased production of

thyroxine File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus rect 66 216 386 25 ...

. However, there are questions as to the relevance of the Gell and Coombs classification of allergic reactions in modern-day understanding of allergy and it has limited utility in clinical practice.

References

External links

{{Use dmy dates, date=May 2019 Hypersensitivity

Examples

See also

References

External links