B & I - Complement Flashcards
what is complement?
a proteolytic activation cascade
what is complement essential for?
innate immunity
what is the most abundant complement component in serum?
C3
how many pathways can complement be activated through?
3
what is the classical pathway of complement mediated by?
antibodies IgM or IgG binding to a microbe surface which is then bound by complement C1
what is the deposition of complement on microbes essential for?
phagocytosis - called opsonisation
what are deposited complexes called?
convertases
what do convertases do?
activate more complement which then deposits to coat the surface
how are convertases bound?
irreversibly bound through a covalent bond
what does cleavage of C3, C4 and especially C5 produce?
small fragments called C3a, C4a and C5a
what are C3a, C4a and C5a known as
chemoattractants called anaphylatoxins
what do anaphylatoxins do
attract and activate neutrophils
what does the end stage of complement (C5 onwards) activate
a lytic pore
what does the lytic pore do
causes some bacteria to lyse
what is the pore known as
membrane attack complex or MAC
what specific type of people are susceptible to chronic infections?
people with deficiencies in a complement component
what protein do many microbes produce
virulence factors
what do virulence factors do
inhibit the complement cascade
what is the alternative pathway
complement C3 is activated just by being close to the surface of the microbe which activates another type of C3 convertase
what are lectins
carbohydrate-binding proteins in the blood that bind to unusual carbohydrates found only on microbes - complement condenses on these bound lectins
neutrophils and macrophages have complement receptors that do what?
bind complement and initiate phagocytosis
