Abstract:Once triggered, complement activation leads to the generation of various C3 degradation products. Receptors for these fragments are expressed by cells of both the innate and adaptive immune system, enabling complement activation to exert both indirect and direct effects on adaptive immune responses. The anaphylatoxin C3a recruits and primes granulocytes and macrophages and influence lymphocyte functions as well. C3 cleavage fragments covalently linked to the antigen influence its fate on the level of the organism and on the level of the cell as well. C3 receptors present on lymphocytes set the threshold for cellular activation and may thereby also shape the immune repertoire.