How does the classical pathway differ from the alternative pathway of complement activation?
The main difference between classical and alternative pathway is that the initiation of alternative pathways is not dependent on the presence of immune complexes. The lectin pathway is activated following the recognition and binding of pathogen-associated molecular patterns (PAMPs) by mannose-binding lectin (MBL) .
What is classical and alternative pathway?
The classical complement pathway typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells.
What are the 3 pathways of complement activation?
Complement can be activated through three pathways: classical, lectin, and alternative. The classical pathway is activated when C1q binds to antibody attached to antigen, activating C1r and C1s, which cleave C4 and C2.
How do the three pathways differ in the substances that can initiate activation?
The three pathways differ in the initial steps of activation, but all three converge to produce a C3 convertase and then a C5 convertase, allowing the formation of the membrane attack complex (MAC) which is responsible for membrane lysis and subsequent pathogen elimination . …
How is the alternative pathway activated?
The alternative pathway (AP) is slowly activated spontaneously by hydrolysis of the internal C3 thioester bond [12–14] and further triggered by contact with various proteins, lipids and carbohydrate structures on microorganisms and other foreign surfaces [1, 15].
What triggers the alternative complement pathway?
The alternative pathway is one of three complement pathways that opsonize and kill pathogens. This pathway is activated by viruses, fungi, bacteria, parasites, cobra venom, immunoglobulin A, and polysaccharides and forms an important part of the defense mechanism independent of the immune response.
How is the alternative pathway of the complement cascade activated?
The alternative pathway is one of three complement pathways that opsonize and kill pathogens. The pathway is triggered when the C3b protein directly binds a microbe. It can also be triggered by foreign materials and damaged tissues.
What is the C5 convertase of the alternative pathway?
C5 convertase of the alternative C pathway is a complex enzyme consisting of three C fragments–one molecule of a major fragment of factor B (Bb) and two molecules of a major fragment of C3 (C3b).
What is the major function of complement system?
The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the innate immune system. The complement system consists of a number of small proteins found in the blood, made by the liver.
How is the classical complement pathway different from the other complement pathways?
The classical pathway is distinct from the other complement pathways in its unique activation triggers and cascade sequence. Activation of the complement pathway through the classical, lectin or alternative complement pathway is followed by a cascade of reactions eventually leading to the membrane attack complex.
How are the classical and alternative pathways activated?
Classical pathway. It is activated by certain isotypes of antibodies bound to antigens; the alternative pathway, which is activated on microbial cell surfaces in the absence of antibody; and the lectin pathway, which is activated by a plasma lectin that binds to mannose residues on microbes.
How is complement activation-classical, alternative and lectin triggered?
Complement Activation- Classical, Alternative and Lectin Pathways 5/5 (2) The lectin pathway is triggered by a plasma protein called mannose-binding lectin (MBL), which recognizes terminal mannose residues on microbial glycoproteins and glycolipids, similar to the mannose receptor on phagocyte membranes described earlier.
Where does complement activation take place in the body?
Complement activation takes place through any of the following three pathways: 1 The classical pathway 2 The alternative pathway 3 The lectin pathway