The anaphylatoxins C3a and C5a, which consist of 77 and 74 amino acids, respectively ), exert a multitude of effects in inflammatory responses. They act as potent chemoattractants for cells such as phagocytes (neutrophils, monocytes) to sites of injury or inflammation. They act as vasodilators and induce smooth muscle contraction. They cause histamine release from mast cells and induce oxidative bursts (consumption of O 2 ) from neutrophils. They are implicated in the production of the cytokine, TNFα, during liver regeneration (Markiewski et al. 2006 ). C3a and C5a exert pleiotropic effects by binding to their respective receptors, namely C3aR and, in the case of C5a, to two receptors, C5aR and C5a receptor-like 2 receptor (C5L2). C5L2 was discovered in 2000 (Ohno et al. 2000) and, although it shares homology with C5aR, its exact biologic function remains unclear.