The Complement System

摘要: The complement system is a central component of innate immunity and plays an important role in pathogen recognition elimination. composed more than 35 soluble membrane-bound proteins. Complement proteins are mainly synthesized by liver hepatocytes circulate throughout the bloodstream. However, both membrane can also be peripheral blood leukocytes, such as neutrophils, macrophages, dendritic cells (DCs). enzymatic cascade serine proteases, which upon activation form proteolytic cascade. activated via classical, lectin, alternative pathway. classical pathway antigenantibody complexes nonimmune molecules, beta-amyloid, prion protein, DNA. lectin pathogen-specific sugars, mannose, fucose, and/or N-acetylglucosamine binding to mannose-binding (MBL) or one ficolins, ficolin-1, ficolin-2, ficolin-3. Although end result MAC assembly, fragments generated mediate wide range biological functions. C1q MBL members family pattern (PRPs) called defense collagens. PRPs bind pathogen-associated molecular patterns (PAMPs) well damageassociated (DAMPs). Under normal physiological conditions, critical clearance apoptotic removal deleterious substances originating from necrotic cells, circulating immune complexes. During course infection, serves extremely effective mechanism for elimination foreign pathogens. uncontrolled host cells. To protect self, organisms have evolved mechanisms complement-mediated activity. highly labile that they undergo spontaneous inactivation if not stabilized other reactions. This allows regulated localized region In addition, prevent damage self-tissue, number fluid-phase regulators. Importantly there regulators at various steps importance best exemplified individuals with deficiency. Individual deficiency components exhibits increased risk infection encapsulated bacteria S. pneumoniae. addition either C1q, C4, C2 linked development autoimmune disorders systemic lupus erythematosus (SLE), this thought failure clear source self-antigens.