Classical complement pathway: Difference between revisions

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=== Regulation of C4b ===

The newly formed C4b cannot stay activated as a highly reactive thioester bond is revealed once C4 has been cleaved. The thioester bond is cleaved by water resulting in its cleavage permanently deactivating the C4b molecule. As a result of this C4b is restricted to only bind to pathogen surfaces. They would undergo rapid deactivation in the time it took to travel from the orgin of activation where C1q is complexed with an antigen-antibody immune complex(IC) or where C1q is directly attached to the pathogens surface.<ref name=":1">{{Cite book |last=Janeway |first=Ca Jr |url=https://www.ncbi.nlm.nih.gov/books/NBK27100/ |title=Immunobiology: The Immune System in Health and Disease |publisher=Garland Science |year=2001 |edition=5th |___location=New York}}</ref>. the pathogen.

=== Formation of C-3 convertase. ===

Surface bound C4b acts as a receptor for the binding of C2.<ref name=":1" />. The binding of C2 and C4b results in C2 being cleaved by C1s into C2a and C2b. C2a diffuses into the plasma as a protein inflammatory mediator while C2b remains attached with C4b forming C4bC2b what is known as C3-convertase, The function of the membrane-bound C3-convertase is the cleavage of many many molecules of C3 into C3a and C3b. C3a is a smaller fragment of C3 is a potent inflammatory mediator.

=== C3b function and structure. ===