Cross-Talk Between Antibodies, IgG Fc Receptors, and the Complement System

Complement is one of the oldest parts of the immune system. It has evolved during the past 1,000 million years to form a network of more than 30 serum and cell surface proteins with pleiotropic functions. Primarily, complement has been considered as an important danger sensing system, recognizing and flagging pathogens and eventually eliminating the intruders. Further, complement senses and eliminates endogenous danger such as apoptotic cells or cell debris. In addition to these well-appreciated properties, complement plays an integral role in the regulation of innate and adaptive immune responses and is involved in tissue regeneration, angiogenesis, lipid metabolism, solubilization and clearance of immune complexes (IC), mobilization of hematopoietic progenitor cells, and neurologic synapse maturation among other functions.