It is not yet clear how complement is activated following fractures, but one may speculate that activation is probably driven by binding of cell debris to C1q, activating the classical or the lectin pathway [ 25, 26].
These activate different complement pathways, with immune complexes typically activating the classical pathway(Ricklin & Lambris, 2013).
A classical and agriculturally relevant plant/microbe interaction is the legume Rhizobium where plant flavonoid compounds control early stages of the symbiosis by activating the rhizobial nod genes.
IKKβ activates the classical pathway by phosphorylating the cytosolic NF-κB binding proteins, IκBs, thereby targeting them for ubiquitin-mediated degradation.
When aggregated or bound to macromolecular ligands, CRP is recognized by complement protein C1q and potently activates the classical complement pathway, engaging C3, the main molecule of adhesion of the complement system, and the terminal membrane attack complex (C5 C9) [ 47].
There are three pathways by which the complement system can be activated: the classical pathway (CP), the alternative pathway (AP) and the lectin pathway (LP).
Notably, Aβ directly activates the classical complement pathway by interacting with C1q protein, triggering a complement cascade that results in the opsonization of plaques [ 129].
Our studies demonstrate the ability of a new Luminex-based assay from Immucor to detect the functional capacity of HLA-Ab to activate the classical complement pathway by measuring C3d deposition (43, 90).
Once bound to the surface of Plasmodium sporozoites, anti-α-gal IgM, IgG2b, and IgG3 mAbs activated the classical pathway of complement, as assessed by C3 deposition.
