C3b may bind to microbial cell surfaces within an organism's body. This can lead to the production of surface-bound C3 convertase and thus more C3b components. Also known as C3bBb, this convertase is similar to soluble C3-convertase except that it is membrane bound.
Alternatively, bound C3b may aid in opsonization of the microbe by macrophages.Complement receptor 1 or CR1 on macrophages allows the engaging of C3b covered microbes.
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