Complement Factor H: Function and Dysfunction

Due to the constant monitoring of its alternate channel, the complement system reacts promptly to threat (AP). Protective membrane-bound and soluble regulators keep an always-on positive-feedback C3b-amplification loop at "tick-over" level on autologous surfaces in the AP. Invading microorganisms exposed surfaces, on the other hand, are quickly opsonized by AP-generated C3b, which tags them for clearance, activates the cytolytic terminal pathway, and releases the anaphylatoxins C3a and C5a. Pathogenic microorganisms, on the other hand, frequently resist complement assault and so escape destruction. Complement factor H is a soluble AP suppressor that recognizes self-surfaces on autologous surfaces, either directly via particular glycosaminoglycan and sialic acid or indirectly via C-reactive protein (CRP), and operates in fluid phase. FH also helps to eliminate damaged cells and cell debris in a non-inflammatory manner. Binding sites, especially for complement receptor (CR3), malondialdehyde (MDA)-modified proteins, and apolipoprotein E (apoE), are dispersed throughout its 20 CCP modules (CCPs), also known as short consensus repeats, to facilitate additional "non-canonical" FH activities. FH-like 1 (FHL-1) is a smaller APregulating splice variation that does not discriminate between self and non-self. The family is completed by six FH-related proteins (FHRs-1-3, 4A and 4B, and 5). These products of genomic duplication events are encoded by a gene cluster located 3' of CFH (CFHR3;CFHR1;CFHR4;CFHR2;CFHR5) and may work against FH.

Author(s): Lily Collins

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