Complement component 5a (C5a) (C5a)

Complement component 5a (C5a) is a 74-amino-acid pro-inflammatory peptide fragment generated by cleavage of complement component C5 by C5 convertase during activation of the complement cascade. It functions as an anaphylatoxin and potent chemoattractant, promoting inflammation by binding to G protein-coupled receptors C5aR1 (CD88) and C5L2 on immune cells such as neutrophils, macrophages, and mast cells, leading to increased vascular permeability, smooth muscle contraction, histamine release, and recruitment of phagocytes to infection sites. C5a enhances innate immunity by upregulating adhesion molecules, integrin avidity, and pro-inflammatory pathways like lipoxygenase and arachidonic acid metabolism, while also modulating IgG Fc receptors to influence adaptive responses. In disease, elevated C5a drives pathology in conditions like sepsis, rheumatoid arthritis, psoriasis, and acute respiratory distress syndrome by inducing neutrophil dysfunction, impairing phagocytosis, and promoting extracellular traps and histone release. Therapeutically, C5a is targeted with antagonists like PMX53 and PMX205, which block C5aR1 to reduce inflammation, though challenges include balancing efficacy against risks of immunosuppression. The query's "Complement component 5 A5-subunit" appears to be a misspelling or misnomer, as no such subunit exists; C5a is the established anaphylatoxin fragment of C5, not a receptor.

Other names

C5a anaphylatoxin

C5a receptor antagonism