Résumé
The major complement component, C3, is the substrate for C3 convertases which emerge by activation of the classical and alternative complement pathways; fragments C3b and C3a are the resulting split products. The C3b becomes a constituent of the amplification C3-convertase in the alternative pathway, and of the C5 convertases responsible for the organization of the potentially cytolytic complex C5b-C9, being also able to interact with numerous serum proteins, cell surface molecules and foreign protein. The C3a functions as mediator of the early events of teh inflamatory process. Recent observations on the molecular features involved in the multiple interaction of C3 characterize this proteins as a most versatile and multifunctional molecule which is also an important participant of both the immune and monimmune surveillance mechanism