"The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane."
A group of blood proteins that work together to help destroy invading microbes.
Anatomy and physiology of the immune system: This topic covers the basic structure and function of the immune system and the role of the complement system in the immune response.
Overview of the complement system: This topic gives a broad overview of the complement system, its components, and overall function in the immune response.
Complement pathways: This topic covers the three main complement pathways – classical, alternative, and lectin – along with their initiators and effectors.
Complement proteins: This topic describes the roles of each of the complement proteins in the different complement pathways, including C1-C9, factor B, factor D, properdin, and others.
Complement activation: This topic covers the different mechanisms of complement activation in each of the complement pathways and how it leads to the formation of the terminal complement complex.
Complement regulation: This topic describes the various mechanisms by which the complement system is regulated to prevent excessive activation and damage to host tissues.
Complement deficiencies: This topic covers the rare genetic disorders associated with complement deficiencies and their clinical manifestations.
Complement in disease: This topic explores the role of the complement system in various disease states, including autoimmune diseases, infections, and inflammatory disorders.
Complement therapeutics: This topic covers the development of complement-targeted drugs for the treatment of complement-related diseases.
Complement and cancer: This topic explores the role of the complement system in cancer development and progression, as well as its potential as a target for cancer immunotherapy.
Classical pathway: It is activated by the binding of immune complexes (antibody-antigen complexes) to C1q, which recruits C1r and C1s to cleave C4 and C2. This leads to the formation of the C3 convertase (C4b2a), which cleaves C3 into C3a and C3b.
Lectin pathway: It is activated by the binding of mannose-binding lectin (MBL) or ficolins to carbohydrates on a pathogen's surface. This recruits MBL-associated serine proteases (MASPs) to cleave C4 and C2, leading to the formation of the C3 convertase.
Alternative pathway: It is continuously active, providing the first line of defense against bacterial and viral infections. It is activated by the spontaneous hydrolysis of C3 into C3a and C3b, which forms the C3 convertase (C3bBb). The amplification of the pathway leads to the formation of the C5 convertase, resulting in the formation of the membrane attack complex (MAC) that can lyse the pathogen's membrane.
"The complement system enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells, promotes inflammation, and attacks the pathogen's cell membrane."
"The complement system is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime."
"The complement system can be recruited and brought into action by antibodies generated by the adaptive immune system."
"The complement system consists of a number of small proteins that are synthesized by the liver and circulate in the blood as inactive precursors."
"When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages."
"The end result of complement activation is stimulation of phagocytes to clear foreign and damaged material, inflammation to attract additional phagocytes, and activation of the cell-killing membrane attack complex."
"About 50 proteins and protein fragments make up the complement system, including serum proteins and cell membrane receptors."
"They account for about 10% of the globulin fraction of blood serum."
"Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway."
"The alternative pathway accounts for the majority of terminal pathway activation."
"Therapeutic efforts in disease have revolved around inhibiting the alternative complement pathway."
"The complement system is also known as the complement cascade."
"The main function of phagocytes in the complement system is to clear foreign and damaged material."
"Yes, complement activation promotes inflammation."
"The role of the membrane attack complex is to kill cells."
"The liver synthesizes the proteins of the complement system."
"Yes, complement activation attracts additional phagocytes."
"Yes, the complement system can attack the pathogen's cell membrane."
"No, the complement system is not adaptable and does not change during an individual's lifetime."