These anaphylatoxins play important roles in the pathogenesis of allergy, autoimmunity, neurodegenerative diseases, cancer and infections through ligation of their receptors, i.e., the C3a receptor (C3aR), C5a receptor 1 (C5aR1), and the C5a receptor-like C5L2 (C5aR2) [17]. The gene discussed is C5AR2; the disease is allergic disease.