Editing Classical complement pathway (section)

=== 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 origin 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 |chapter=The complement system and innate immunity |publisher=Garland Science |year=2001 |edition=5th |location=New York}}</ref>