Complement Activation: Part 1

Question 1

A _________ is a system of proteins that are activated by the presence of a ________, that are made up of predominantly inert until activation.

Answer 1

Complement

Pathogen

Question 2

A key site of activation of complements, is at the ______ of pathogens, which can proceed into 3 pathways.

Answer 2

Surface

Question 3

What are the 3 pathways of the complement system?

Answer 3

Classical, Lectin, and Alternative

Question 4

What are the possible outcomes of the complement system?

Answer 4

Opsonization, MACs, or recruitment of inflammatory and immunocompetent cells

Question 5

True or False: Some complements are capable of acting as chemoattractants during chemotaxis for phagocytic cells.

Answer 5

True

Question 6

How does the complement also capable of activating the adaptive immune response?

Answer 6

Opsonization by APC’s (dendritic cells, macrophages, and B cells)

Question 7

What is the correct order of discovery for the complement proteins 1 - 9?

Answer 7

C1, C4, C2, C3, C5, C6, C7, C8, C9

Question 8

While more often, the larger fragment of complement proteins will be given the “b,” the larger complement protein of C2 is _ and the smaller is _.

Answer 8

C2a = larger
C2b = smaller

Question 9

The alternative pathway employs complement proteins that begin with different capital letters. Will the a fragment be smaller, or will the b fragment be larger?

Answer 9

a = smaller
b = larger

Question 10

Describe the initiation of the classical pathway.

Answer 10

C1q proteins will bind to the surface of a pathogen (lipoteichoic acid, CRPs on phosphocholine, Ag:Ab complexes).

Question 11

Describe the initiation of the lectin pathway.

Answer 11

MBL binds to pathogen surfaces or ficolins to N-acetylglucosamine

Question 12

Describe the initiation of the alternative pathway.

Answer 12

C3b proteins binding to pathogen surfaces

Question 13

All the pathways of the complement system lead to the production of what protein complex? Where will it bind to?

Answer 13

C3 convertase, which binds to pathogen surfaces

Question 14

What is the role of C3 convertase?

Answer 14

The production of C3a (mediates inflammation) and C3b (main molecule)

Question 15

C3b acts as an ______, which marks the pathogen as a target for phagocytosis.

Answer 15

Opsonin

Question 16

In order to form C5 convertase, what molecules must bind together on the surface of the pathogen?

Answer 16

C3b and C3 convertase

Question 17

What are the products of C5’s interaction with C5 convertase?

Answer 17

C5a (an inflammatory mediator) and C5b (main molecule)

Question 18

C5b leads to the formation of the -?

Answer 18

Membrane attack complex

Question 19

How many Ig’s of IgM and IgG are needed to bind to an antigen, so that its Fc region can bind to the complement protein __?

Answer 19

One IgM, several IgG

C1 or C1qr2s2

Question 20

The C1q backbone has six domains, with two copies of the ____ and ____ domains.

Answer 20

C1r and C1s

Question 21

Explain how C1 is activated.

Answer 21

C1q binds to 2 adjacent Fc regions of antibodies, which activates C1r that cleaves itself and then C1s, which activates it

Question 22

What function does C1s have?

Answer 22

It cleaves C4, and this leads the C4b fragment to attach to the Ag:Ab complex or microbe

It cleaves C2, where C2a will bind to C4b

Question 23

What molecular name does C4b2a have?

Answer 23

C3 convertase

Question 24

C3 convertase will cleave C3, which will lead to C3b -?

Answer 24

Binding to C3 convertase, to form C5 convertase (C4b2a3b)

Question 25

C5 convertase leads to the formation of the _________ ______ _______.

Answer 25

Membrane Attach Complex