Complement System Effector Functions

Complement System Effector Functions

Complement System Effector Functions

Historically, the term complement was used to refer to a heat-labile serum component that was able to lyse bacteria (activity is destroyed (inactivated) by heating serum at 56 degrees for 30 minutes). However, complement is now known to contribute to host defenses in other ways as well. Complement can opsonize bacteria for enhanced phagocytosis; it can recruit and activate various cells including polymorphonuclear cells (PMNs) and macrophages; it can participate in regulation of antibody responses and it can aid in the clearance of immune complexes and apoptotic cells. Complement can also have detrimental effects for the host; it contributes to inflammation and tissue damage and it can trigger anaphylaxis.

Complement comprises over 20 different serum proteins that are produced by a variety of cells including, hepatocytes, macrophages and gut epithelial cells. Some complement proteins bind to immunoglobulins or to membrane components of cells. Others are proenzymes that, when activated, cleave one or more other complement proteins. Upon cleavage some of the complement proteins yield fragments that activate cells, increase vascular permeability or opsonize bacteria.

Complement system is a highly regulated and multifunctional system that is the major extracellular arm of innate immunity. Its activation results in three major potential outcomes for microbes: cell lysis upon assembly and insertion of the terminal membrane attack complex (MAC), complement mediated opsonization, and the release of anaphylatoxins that enhance local inflammation.

Antibodies that bind to surface antigens (for example, on bacteria) will attract the first component of the complement cascade with their Fc region and initiate activation of the classical pathway of complement system. This results in the killing of bacteria in two ways. First, the binding of the antibody and complement molecules marks the microbe for ingestion by phagocytes in a process called opsonization; these phagocytes are attracted by certain complement molecules generated in the complement cascade. Second, some complement system components form a membrane attack complex(MAC) to assist antibodies to kill the bacterium directly (bacteriolysis).

Complement System Effector Functions References

1. Clay C D, et al. (2008). Evasion of complement-mediated lysis and complement C3 deposition are regulated by Francisella tularensis lipopolysaccharide O antigen. The Journal of Immunology, 181(8), 5568-5578.
2. Ravetch J V, et al. (2001). Igg fc receptors. Annual review of immunology, 19(1), 275-290.
3. Rus H, et al. (2005). The role of the complement system in innate immunity. Immunologic research, 33(2), 103-112.

Complement System
Complement System Overview
What is Complement System
How Does Complement System Work
Complement Protein Fragment Nomenclature
Complement System Component / Protein Regulator and Receptor
Complement Component / Protein of Complement System
Complement Regulator of Complement System: RCA/CCP family
Complement Regulator of Complement System: Others
Complement Receptors of Complement System
Complement Genetic Feature
Regulator of complement activation / RCA Gene Cluster
Complement MAC Gene Cluster
Complement MHC Class III Gene Cluster
Complement Activation Pathways
Complement Activation Definition
Complement Activation Classical Pathway
Complement Activation Alternative Pathway
Complement Activation Lectin Pathway
Serine Proteases of Complement Activation Pathway
Complement System Role
Complement System and Direct Interactions
Complement System Function in Immune System
Complement-Dependent Cytotoxicity/CDC
Therapeutic Target of Complement System
Complement System and Toll-like Receptors / TLRs
Complement System and Coagulation
Complement Cascade and Inhibitors
Complement Evasion of Pathogens
Complement System and Antimicrobial Peptides/AMPs
Complement System and Diseases
Complement System and Cancer
Complement System and Rheumatic Diseases
Complement Receptor 1 / CR1 and Alzheimer's Disease / AD
Complement System and Autoimmune Diseases
Complement System and Age-Related Macular Degeneration/AMD
Complement System and Schizophrenia
Complement System Deficiency Diseases
Classical Pathway Deficiency
Alternative Pathway Deficiency
Complement Receptor Deficiency
Mannose-Binding Lectin / MBL Pathway Deficiency
Membrane Attack Complex/MAC Deficiency
Total Complement Activity / CH50 / CH100
Complement System Structure
Complement Membrane Attack Complex/MAC
Complement Component / Protein Structure
Complement Regulator Structure
Complement Receptor Structure
Collectins and Ficolins: Humoral Lectins of the Innate Immune System
Complement System Effector Functions
Complement Mediated Opsonization
Complement Mediated Cell Lysis
Complement Mediated Phagocytosis
Complement Mediated Inflammation
Complement Mediated Chemotaxis
Complement Mediated Antibody Formation
Anti-Complement Antibody Products