Preferred Label : Alternative Complement Pathway;
Alternative definition : BIOCARTA: The complement system of plasma proteins is an important part of the immune
system that forms a cascade of factors that lyses foreign cells. There are two branches
of the complement system, the classical pathway that is initiated by antibody-antigen
complexes on a cell and the alternative pathway that is antibody independent. The
ultimate result in either pathway is the creation of the membrane attack complex,
a large pore in the cell membrane that results in cell lysis. The alternative pathway
starts with the spontaneous conversion of C3 to an active protease. C3 contains a
thioester group that is spontaneously hydrolyzed at a slow rate to create C3(H2O).
From there, binding of factor B (Fb) and activation by factor D (Fd) cleaves factor
B to create the active protease C3 convertase (AP convertase). This enzyme cleaves
C3 to form C3b, which can go on to form a C5 activating convertase. At this point
the alternative pathway proceeds in the same manner as the classical pathway, recruiting
additional complement factors (C6, C7, C8 and C9) to ultimately form the membrane
attack complex and lyse the associated cell. One question about the alternative pathway
is how the spontaneous activation of C3 in plasma leads to the lysis of specific cells
in the absence of antibody on the cell surface. Active C3b binds to the cell surface,
particularly to complement activators like cell wall components and lipopolysaccharide.
A constant low level of spontaneous C3b formation ensures that C3b can bind to invading
cells and trigger the rest of the alternative complement pathway to lyse the cells
even in the absence of an antibody response. The constant low level of C3b activation
and potential activation of the alternative pathway is kept in check by a natural
damper, factor H and factor I. Factors H and I in plasma inactivate C3b enzyme in
solution. Factors H and I cannot inactivate C3b on the cell surface due to protection
by properdin, ensuring that the alternative pathway is primarily inactive in plasma
and specifically activated on the surface of invading. (This definition may be outdated
- see the DesignNote.);
NCIt note : The BIOCARTA Definition (ALT_DEFINITION) for this pathway concept was provided by
BioCarta. This property was not created by, nor is it maintained by the NCI Thesaurus
staff. Additionally, BioCarta is no longer updating its pathway data; thus, the BIOCARTA
Definition might be outdated or inaccurate. Please see the Terms and Conditions for
Use at http://www.biocarta.com/.;
Biocarta ID : h_alternativePathway;
Origin ID : C38983;
UMLS CUI : C0009546;
- Automatic exact mappings (from CISMeF team)
- Currated CISMeF NLP mapping
- Semantic type(s)
- UMLS correspondences (same concept)
- has_gene_product_element
- pathway_has_gene_element