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'''Complement factor B''' ('''CFB''') is a protein that plays a crucial role in the [[innate immune system]], specifically within the [[alternative pathway]] of the [[complement system]]. The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear pathogens from an organism. Complement factor B is a component of the [[C3 convertase]] enzyme, which is central to the activation of the complement system.
{{DISPLAYTITLE:Complement factor B}}


==Structure and Function==
== Complement factor B ==
Complement factor B is a glycoprotein synthesized in the liver and found in the blood plasma. It is composed of a light chain and a heavy chain, which are linked by a disulfide bond. The protein is initially produced as a single polypeptide chain (pro-factor B) that is cleaved into its active form by the enzyme [[factor D]]. The active form of complement factor B then associates with [[C3b]], a fragment of complement component 3, to form the active C3 convertase of the alternative pathway, C3bBb. This enzyme complex cleaves C3 into C3a and C3b, propagating the complement activation cascade that leads to the opsonization of pathogens, recruitment of inflammatory cells, and eventual lysis of the target cells.


==Genetics==
[[File:Droga_alternatywna.png|thumb|right|Diagram of the alternative pathway of complement activation, showing the role of complement factor B.]]
The gene encoding complement factor B is located on chromosome 6 in humans. Mutations in this gene can lead to deficiencies or dysregulation of the complement system, which can result in increased susceptibility to infections, autoimmune diseases, or other immune-related conditions.


==Clinical Significance==
'''Complement factor B''' is a crucial component of the [[complement system]], which is part of the [[innate immune system]]. It plays a significant role in the [[alternative pathway]] of complement activation, which is one of the three pathways that activate the complement system, the others being the [[classical pathway]] and the [[lectin pathway]].
Alterations in the activity or concentration of complement factor B can have significant clinical implications. Overactivity of the complement system, including excessive activation of complement factor B, can contribute to the pathology of autoimmune diseases such as [[systemic lupus erythematosus]] (SLE) and [[age-related macular degeneration]] (AMD). Conversely, deficiencies in complement factor B can lead to an increased risk of infections, particularly those caused by encapsulated bacteria.


In addition to its role in disease, complement factor B is also a target for therapeutic intervention. Inhibitors of complement factor B are being explored as potential treatments for diseases characterized by excessive complement activation.
== Structure ==


==Diagnostic Use==
Complement factor B is a single-chain [[glycoprotein]] that circulates in the blood plasma. It is synthesized primarily in the [[liver]] and consists of several domains, including a von Willebrand factor type A domain, a serine protease domain, and a complement control protein domain. These domains are essential for its function in the complement cascade.
Measurement of complement factor B levels, along with other components of the complement system, can be used in the diagnosis and monitoring of diseases associated with complement system dysregulation. Elevated or decreased levels of complement factor B can provide clues to the underlying pathology of various conditions.
 
== Function ==
 
In the alternative pathway, complement factor B binds to [[C3b]], a fragment of the complement component [[C3]], forming a complex known as C3bB. This complex is then cleaved by the enzyme [[factor D]] to form C3bBb, which is a potent [[C3 convertase]]. The C3 convertase amplifies the complement response by cleaving additional C3 molecules into C3a and C3b, leading to a cascade of events that result in the opsonization of pathogens, recruitment of inflammatory cells, and formation of the [[membrane attack complex]].
 
== Regulation ==
 
The activity of complement factor B is tightly regulated to prevent damage to host tissues. Regulatory proteins such as [[factor H]] and [[decay-accelerating factor]] (DAF) help to control the activity of the C3 convertase by promoting the dissociation of C3bBb and facilitating the degradation of C3b.
 
== Clinical significance ==
 
Dysregulation of complement factor B can lead to various [[diseases]]. Overactivation of the alternative pathway is implicated in conditions such as [[atypical hemolytic uremic syndrome]] (aHUS), [[age-related macular degeneration]] (AMD), and [[paroxysmal nocturnal hemoglobinuria]] (PNH). Conversely, deficiencies in factor B can result in increased susceptibility to infections due to impaired complement activation.
 
== Related pages ==


==See Also==
* [[Complement system]]
* [[Complement system]]
* [[Innate immune system]]
* [[Alternative pathway]]
* [[Autoimmune diseases]]
* [[Factor D]]
* [[Opsonization]]
* [[Factor H]]
 
* [[Membrane attack complex]]
[[Category:Immune system]]
[[Category:Proteins]]
[[Category:Glycoproteins]]


{{Medicine-stub}}
[[Category:Complement system]]

Latest revision as of 05:32, 16 February 2025


Complement factor B[edit]

Diagram of the alternative pathway of complement activation, showing the role of complement factor B.

Complement factor B is a crucial component of the complement system, which is part of the innate immune system. It plays a significant role in the alternative pathway of complement activation, which is one of the three pathways that activate the complement system, the others being the classical pathway and the lectin pathway.

Structure[edit]

Complement factor B is a single-chain glycoprotein that circulates in the blood plasma. It is synthesized primarily in the liver and consists of several domains, including a von Willebrand factor type A domain, a serine protease domain, and a complement control protein domain. These domains are essential for its function in the complement cascade.

Function[edit]

In the alternative pathway, complement factor B binds to C3b, a fragment of the complement component C3, forming a complex known as C3bB. This complex is then cleaved by the enzyme factor D to form C3bBb, which is a potent C3 convertase. The C3 convertase amplifies the complement response by cleaving additional C3 molecules into C3a and C3b, leading to a cascade of events that result in the opsonization of pathogens, recruitment of inflammatory cells, and formation of the membrane attack complex.

Regulation[edit]

The activity of complement factor B is tightly regulated to prevent damage to host tissues. Regulatory proteins such as factor H and decay-accelerating factor (DAF) help to control the activity of the C3 convertase by promoting the dissociation of C3bBb and facilitating the degradation of C3b.

Clinical significance[edit]

Dysregulation of complement factor B can lead to various diseases. Overactivation of the alternative pathway is implicated in conditions such as atypical hemolytic uremic syndrome (aHUS), age-related macular degeneration (AMD), and paroxysmal nocturnal hemoglobinuria (PNH). Conversely, deficiencies in factor B can result in increased susceptibility to infections due to impaired complement activation.

Related pages[edit]

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