Function 
Complement C5 (CC5) is the fifth component of the complement system.  The complement system is part of the innate immune system.  CC5 is composed of α chain (C5a) and β chain (C5b).  Proteoplytic degradation of CC5 produces  which is a mediator of local inflammatory process.  The C terminal domain of CC5 (residues 1530-1676) is homologous to a domain in netrins and is named .  Activation of CC5 by C5 convertase initiates the assembly of the C5 to C9 components into the membrane attack complex. [1]
  Disease 
Mutations in CC5 cause a deficiency leading to severe recurrent infections and are linked to liver fibrosis, Leiner's disease and rheumatoid arthritis.