The Complement System

Question 1

is the complement part of innate or acquired immune responses, or both?

Answer 1

effector arm of both

Question 2

what are opsonins?

Answer 2

molecules that enhance the ability of immune cells to phagocytose material

Question 3

what are the complement components that are peptides that induce local and systemic inflammatory responses?

Answer 3

anaphylatoxins
C3a, C4a, C5a do this

Question 4

do complement components directly kill pathogens?

Answer 4

yes, some of them do

Question 5

what are the ways that a pathogen gets recognized by the complement system?

Answer 5

classical pathway: triggered by antibodies bound to antigens on a pathogen
alternative pathway: triggered by macromolecules on pathogen cell surfaces
lectin pathway: initiated when lectin binds to carbohydrates on the surface of pathogens

Question 6

what happens after the complement system is activated?

Answer 6

recruitment of inflammatory cells
opsonization of pathogens
lysis and death of pathogens

Question 7

which pathway is the major effector pathway of the adaptive immune response?

Answer 7

classical complement pathway

Question 8

in the classical pathway, what is the first step?

Answer 8

C1 binds to the Fc region of an antibody leading to the generation of a C1 protease enzyme

Question 9

what does C1 protease act on during the classical pathway (step 2)?

Answer 9

C4 and C2 to yield a and b fragments of each
C4b binds covalently to the cell surface of a target (along with C2b) (C4bC2b complex)

Question 10

what does the C4bC2b complex do (classical pathway) (step 3)?

Answer 10

acts on C3 to become C3 convertase

Question 11

how is the C5 convertase formed (step 4 of classical pathway)?

Answer 11

C3 convertase clease C3 into C3a and C3b, C3b binds with C4b2b to form C4b2b3b: C5 convertase

Question 12

is the alternative pathway of complement an effector arm of innate or adaptive immunity?

Answer 12

innate immune response

Question 13

what happens in the first step of the alternative pathway?

Answer 13

C3 converts to C3a and C3b by slow spontaneous hydrolysis

Question 14

what does C3b do in alternative pathway (step 2)?

Answer 14

binds to foreign surface antigens
combines with serum protein factor B to form C3bB

Question 15

what is the alternative pathway C3 convertase (step 3)?

Answer 15

Factor D cleaves C3bB to form C3bBb, a C5 convertase

Question 16

what two things can activate the lectin binding pathway?

Answer 16

mannose-binding lectin (binds to terminal mannose)
ficolin proteins (bind to N-acetylglucosamine residues on surface of some pathogens)

Question 17

is the lectin binding pathway innate or adaptive immune response?

Answer 17

innate

Question 18

after the binding in the lectin binding pathway, what gets activated and what do they do (step 1)?

Answer 18

mannose-associated serine protease (MASP) 1 and 2
cleaves C2 and C4

Question 19

in the lectin binding pathway, what do C2b and C4b do?

Answer 19

form C3 convertase, cleaving it into C3a and C3b to form C5 convertase (C4b2b3b)

Question 20

what do the C5 convertases do (from all the pathways)?

Answer 20

cleave C5 into a and b, leading to a pore in the membrane (C6, 7, 8, 9)

Question 21

what is opsonization in complement?

Answer 21

phagocytosing microorganisms
macrophages and neutrophils express CRI, and cell-surface receptor, that receive microorganisms that have been coated with C3b

Question 22

what fragments lead to inflammation at the site of activation of the complement?

Answer 22

C3a, C4a, and C5a

Question 23

what does mannin binding lectin lead to?

Answer 23

viral neutralization through opsonization and lysis or blocking the virus from entering cells

Question 24

what removes immune complexes?

Answer 24

macrophages in the liver and spleen

Question 25

how many proteins play a major part in the complement system?

Answer 25

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