Alternative complement pathway

The Alternative complement pathway (pronounced: al-ter-na-tive kom-ple-ment path-way) is a component of the immune system that enhances the ability of antibodies and phagocytic cells to clear microorganisms and damaged cells from an organism, promotes inflammation, and attacks the pathogen's cell membrane. It is one of three complement pathways that opsonize antigens and induce a series of inflammatory responses that help to fight infections.

Etymology

The term "alternative" refers to the fact that this pathway is an alternative to the other two complement pathways: the classical complement pathway and the lectin pathway. The word "complement" is derived from the concept that these systems "complement" the antibacterial activity of antibodies. The term "pathway" refers to the sequence of reactions that lead to the activation of the complement system.

Activation

The alternative complement pathway is continuously activated at a low level, but its activity is amplified when pathogens are detected. It is initiated by the spontaneous hydrolysis of the complement component 3 (C3) protein, which binds to factors B and D to form the initial C3 convertase. This process does not require the presence of antibodies, distinguishing it from the classical and lectin pathways.

Regulation

The alternative complement pathway is tightly regulated by several proteins, including Factor H, Factor I, and properdin. These proteins prevent the pathway from causing excessive damage to host tissues.

Clinical significance

Dysregulation of the alternative complement pathway has been implicated in a variety of diseases, including atypical hemolytic uremic syndrome (aHUS), age-related macular degeneration (AMD), and C3 glomerulopathy.

References

External links

Medical encyclopedia article on Alternative complement pathway
Wikipedia's article - Alternative complement pathway

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Alternative complement pathway