Overview Introduction The complement system is a group of circulating proteins that login to view 5 more bullets The system can be activated in one of three ways including login to view 6 more bullets Activation of the complement pathway leads to login to view 4 more bullets Complement must be closely controlled by inhibitors such as login to view 2 more bullets Activation of Complement Complement Activation Pathways Feature Classical Alternative Lectin Detects Surfaces with bound antibodies (IgG and IgM) Surfaces not protected by complement inhibitors Surfaces with mannose Specificity Conferred by the specific binding of antibodies Conferred by inactivation of complement by host inhibitors Conferred by lack of mannose on host membranes Initiating factor C1q C1rC1s C1s C3 factor turnover Factor D Mannose binding lectin and associated proteases C3 convertase C4b C2b C3b Factor Bb C4b C2b Functions The complement cascade has many functions including login to view 15 more bullets Together these effects of the complement cascade are important in login to view 3 more bullets Complement Component Deficiencies Complement Component Deficiencies Missing Factor Presentation Pathology Circulating C3 Recurrent infection by pyogenic bacteriaIncreased susceptibility to type III hypersensitivity reactions Failure of C3 convertase formation Lack of immune complex and pathogenic bacterial clearance C5, C6, C7, C8, or C9 Increased susceptibility to recurrent Neisseria infections Failure of membrane attack complex formation C1 esterase inhibitor Hereditary angioedema ACE inhibitors are contraindicated Unregulated activation of kallikrein by complement system leading to increased bradykinin activity Decay accelerating factor (CD55) Paroxysmal nocturnal hemoglobinuria Unregulated activation of complement leads to lysis of red blood cells