334 Complement system

Name the stages of complement activation

Answer explanation

Activation via PRR, complement cascade (C3 convertase) amplification, Inflammation, phagocytosis, membrane attack

Name the 3 complement pathways

Answer explanation

Classical pathway, alternative pathway, lectin pathway

Compare and contrast the 3 complement pathways

Answer explanation

The pathways main differences relies on the way in which they are activated alongside how they are regulated. The lectin pathway is activated via detection of carbs present on the surface of pathogens. The classical pathway is activated by Ag/Ab complexes being activated. The alternative pathway is activated by spontaenous hydrolysis of the C3 subunit. They are similar in the fact that they each result in C3 convertase activation and subsequent inflammation, opsonization, and lysis occurs

What are the 3 activating factors for the complement pathways?

Answer explanation

Carb complex, Ag/Ab complex, spontaneous hydrolysis of C3

Describe how negative and positive regulation of the complement pathways are achieved

Answer explanation

Negative regulation is achieved by reducing the available subunits of C3b by producing proteins that bind C3b in the alternative pathway. Positive regulation through the lectin and classical pathways is done via production of supporting proteins C1r and MASP1 and 2 which aid at different steps during the complement pathway

Describe the events following C3 convertase formation

Answer explanation

C3 convertase cleaves C3 into C3a, and C3b. C3a is released and induces inflammation, while C3b remains and enhances phagocytosis. Some C3b will bind with remaining C3 convertase and produce C5 convertase. This will cleave C5 into C5a and C5b. C5a further enhances phagocytosis while C5b will begin the process of pore formation for lysis of pathogen membrane

Explain how the outcomes of the complement pathway work

Answer explanation

Post C3 convertase, 3 outcomes are produced, being inflammation, opsonization, and lysis. Inflammation is increased at the site of infection due to the products C3a, 4a, and 5a all being produced. These act upon blood vessels to increase permeability. Opsonization also occurs in which C3b binds to Ag surfaces and enhances phagocytosis, but the phagocytes must have a C3b receptor. Finally, complement proteins from C5b through to C9 form a pore complex on the membrane surface of pathogens and creates a hole in the membrane.