Complement deficiency
Encyclopedia
Complement deficiency is an immunodeficiency
of absent or suboptimal functioning of one of the complement system
proteins.
The disorders can be divided into two categories:
Because there are redundancies in the immune system
, many complement disorders are never diagnosed. A recent study estimated that less than 10% are identified.
These levels can be used to distinguish conditions:
Immunodeficiency
Immunodeficiency is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Immunodeficiency may also decrease cancer immunosurveillance. Most cases of immunodeficiency are acquired but some people are born with defects in their immune system,...
of absent or suboptimal functioning of one of the complement system
Complement system
The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime...
proteins.
The disorders can be divided into two categories:
- Disorders of the proteins that act to inhibit the complement system (such as C1-inhibitorC1-inhibitorC1-inhibitor is a protease inhibitor belonging to the serpin superfamily. Its main function is the inhibition of the complement system to prevent spontaneous activation. C1-inhibitor is an acute-phase protein that circulates in blood at levels of around 0.25 g/L. The levels rise ~2-fold during...
) can lead to an overactive response, causing conditions such as hereditary angioedemaHereditary angioedemaHereditary angioedema presents in the second to fourth decade, and is characterized by local swelling in subcutaneous tissues....
and hemolytic-uremic syndromeHemolytic-uremic syndromeHemolytic-uremic syndrome , abbreviated HUS, is a disease characterized by hemolytic anemia, acute renal failure and a low platelet count . It predominantly, but not exclusively, affects children. Most cases are preceded by an episode of diarrhea caused by E. coli O157:H7, which is acquired as a...
.
- Disorders of the proteins that act to activate the complement system (such as C3C3 (complement)Complement component 3, often simply called C3, is a protein of the immune system. It plays a central role in the complement system and contributes to innate immunity. In humans it is encoded on chromosome 19 by a gene called C3.-Function:...
) can lead to an underactive response, causing greater susceptibility to infections.
Because there are redundancies in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, many complement disorders are never diagnosed. A recent study estimated that less than 10% are identified.
Hypocomplementemia
The term "hypocomplementemia" is a more general term used to describe decreased complement levels. The term "secondary complement disorder" is sometimes used to refer to low complement levels that are not directly due to a genetic cause but secondary to another medical condition.These levels can be used to distinguish conditions:
- Systemic lupus erythematosusSystemic lupus erythematosusSystemic lupus erythematosus , often abbreviated to SLE or lupus, is a systemic autoimmune disease that can affect any part of the body. As occurs in other autoimmune diseases, the immune system attacks the body's cells and tissue, resulting in inflammation and tissue damage...
causes low C3 and C4Complement component 4Complement component 4 is a protein involved in the complement system.It is cleaved into proteins 4a and 4b.* C4a is an anaphylatoxin.* C4b forms part of C3-convertase, in conjunction with 2a:* C4b can bind CR1.... - Membranoproliferative glomerulonephritisMembranoproliferative glomerulonephritisMembranoproliferative glomerulonephritis , also known as mesangiocapillary glomerulonephritis, is a type of glomerulonephritis caused by deposits in the kidney glomerular mesangium and basement membrane thickening, activating complement and damaging the glomeruli.MPGN accounts for approximately 4%...
causes low C3, but normal C4