[3] Every cell in the human body is protected by one or more of the membrane-associated RCA proteins, CR1, DAF or MCP.
[5] For example, C3b.Bb is an important convertase that is part of the alternative pathway, and it is formed when factor B binds C3b and is subsequently cleaved.
Recently, it has been demonstrated that the order, spatial relationship, and structure of these domains is essential for determining function.
There are two primary mechanisms by which dysfunction of complement can contribute to tissue damage:[12] The importance of complement regulation for good health is highlighted by recent work that seems to imply that individuals carrying point mutations or single nucleotide polymorphisms in their genes for factor H may be more susceptible to diseases including atypical hemolytic uremic syndrome,[13] dense deposit diseases (or membranoproliferative glomerulonephritis type 2) and - most notably because of its prevalence in the elderly - age-related macular degeneration.
However, some malignant cells have been shown to have increased expression of membrane-bound complement control proteins, especially CD46, DAF and CD59.
Many viruses, such as Vaccinia incorporate mimics of CCPs into their envelope for the purposes of evading the complement system.
Still other microbes such as the measles virus use CCPs as receptors to gain entry to cells during infection.
Certain forms of schizophrenia are characterised by an underlying biological mechanism of excessive synaptic pruning, mediated by a dysregulated complement system in the brain.