Factor present in final common terminal complement pathway
Ref Harrison 17/e p2030 _2032 C5a is a protein fragment released from cleavage of complement component C5 by protease C5-convease into C5a and C5b fragments. C5b is impoant in late events of the complement cascade, an orderly series of reactions which coordinates several basic defense mechanisms, including formation of the Membrane Attack Complex (MAC), one of the most basic weapons of the innate immune system, formed as an automatic response to intrusions from foreign paicles and microbial invaders. It essentially pokes microscopic pinholes in these foreign objects, causing loss of water and sometimes death. C5a, the other cleavage product of C5, acts as a highly inflammatory peptide, encouraging complement activation, formation of the MAC, attraction of innate immune cells, and histamine release involved in allergic responses
C4
C3
C5
Protein B
General anatomy