C3b

The classical and alternative complement pathways.

C3b is the larger of two elements formed by the cleavage of complement component 3. C3b covalently bonds to microbial cell surfaces within an organism's body. This leads to the production of surface-bound C3-convertase and thus more C3b components. Bound C3b also aids in opsonization of the microbe by macrophages.^[1] Complement receptor 1 (CR1) on macrophages allows the engaging of C3b covered microbes. C3b also aids in the clearance of immune complexes (antigen-antibody).

C3b is cleaved into C3c and C3d.

References

↑ Immunology at MCG 1/phagocyt

External links

http://www.merck.com/mmpe/sec13/ch163/ch163d.html

Proteins: complement system (C, L, A)

Activators/enzymes

Early	C: C1Q/C1R/C1S C4 C4a C2 L: MASP1/MASP2 MBL A: Factor B Factor D Factor P/Properdin

Middle	C3 C3a C3b/iC3b C5 C5a C3-convertase C5-convertase

Late	MAC C6 C7 C8 C9

Inhibitors

CL: C4BP

A: Factor H

Complement receptors

Index of the immune system

Description	Physiology cells autoantigens autoantibodies complement surface antigens IG receptors

Disease	Allergies Immunodeficiency Immunoproliferative immunoglobulin disorders Hypersensitivity and autoimmune disorders Neoplasms and cancer

Treatment	Procedures Drugs antihistamines immunostimulants immunosuppressants monoclonal antibodies