Type II hypersensitivity, in the
Gell and Coombs classification of allergic reactions, is an antibody-mediated process in which
IgG and
IgM 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, tissue damage or loss of function through mechanisms such as
# complement activation via the
classical complement pathway
#
Antibody-dependent cellular cytotoxicity 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 morphology (linguistics), morphological process in which words are formed by stringing together morphemes (word parts), each of which corresponds to a single Syntax, syntactic feature. Languages that use agglu ...
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 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 (red blood cells). For human blood transfusions, it is the most important of the 47 different blood type (or group) cla ...
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, 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, also known as toxic diffuse goiter or Basedow's disease, 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 thyroid. ...
, in which anti-thyroid stimulating hormone receptor antibodies lead to increased production of
thyroxine
Thyroxine, also known as T4, is a hormone produced by the thyroid gland. It is the primary form of thyroid hormone found in the blood and acts as a prohormone of the more active thyroid hormone, triiodothyronine (T3). Thyroxine and its acti ...
.
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.
See also
*
Type I hypersensitivity
Type I hypersensitivity (or immediate hypersensitivity), in the Hypersensitivity, Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type ...
*
Type III hypersensitivity
Type III hypersensitivity, in the Gell and Coombs classification of allergic reactions, occurs when there is accumulation of immune complexes (antigen-antibody complexes) that have not been adequately cleared by innate immune cells, giving ris ...
*
Type IV hypersensitivity
Type IV hypersensitivity, in the Gell and Coombs classification of allergic reactions, often called delayed-type hypersensitivity, is a type of hypersensitivity reaction that can take a day or more to develop. Unlike the other types, it is not ...
References
External links
{{Use dmy dates, date=May 2019
Hypersensitivity