Complement component C8 plays a pivotal role in the formation of the membrane attack complex (MAC), an important antibacterial immune effector. C8 initiates membrane penetration and coordinates MAC pore formation. MAC is generated by sequential addition of C5b, C6, C7, C8, and C9 molecules, which results in the transmembrane pore and eventual cell lysis. After binding to C8,C5b-7 complex, by itself transiently bound to membrane surface and nonfunctional, is endowed with the ability to cause membrane damage and polymerization of C9 that greatly accelerate MAC activity.
Complement component 8 deficiency is a disorder that causes the immune system to malfunction, resulting in a form of immunodeficiency. Immunodeficiencies are conditions in which the immune system is not able to protect the body effectively from foreign invaders such as bacteria. People with complement component 8 deficiency have a significantly increased risk of recurrent bacterial infections, particularly by a bacterium called Neisseria meningitidis. Although meningitis can be life-threatening, individuals with complement component 8 deficiency are less likely to die from the infection than people in the general population who contract it.
There are two types of complement component 8 deficiency, types I and II, classified by their genetic cause. The two types have the same signs and symptoms. In addition, Complement component 8 deficiency is a rare disorder, although its prevalence is unknown. Type I occurs in several populations, particularly in people with Hispanic, Japanese, or African Caribbean heritage, whereas type II primarily occurs in people of Northern European descent.
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