Complement

Question 1

What is complement?

Answer 1

group of serum and cell surface proteins activated by factors such as the combination of antigen and antibody that results in the generation of enzyme cascades leading to a variety of biological consequences

Question 2

What are the three pathways that initiate the complement cascade?

Answer 2

classical, lectin, and alternative

Question 3

When is the classical pathway initiated?

Answer 3

when IgM and IgG binds to antigen

Question 4

What does the binding of IgM and IgG to the antigen in the classical pathway allow for?

Answer 4

the conformational change of the antibody to the Fc portion to allow for C1 to bind

Question 5

When is the binding site open in the classical pathway?

Answer 5

only when the antibody is bound to the antigen

Question 6

Would you classify the classical pathway as innate or adaptive?

Answer 6

both: the innate arm (complement) is working with the adaptive system (antibody)

Question 7

What is the lectin pathway initiated by?

Answer 7

soluble pattern recognition molecules; specifically mannose binding lectin

Question 8

Is the lectin pathway innate or adaptive?

Answer 8

innate

Question 9

What is the alternative pathway initiated by?

Answer 9

the binding of C3b onto the cell wall and then another complement protein

Question 10

What can C3b bind to?

Answer 10

the cell wall of bacteria, fungi and some viruses

Question 11

What is the most important molecule to initiate the complement cascade?

Answer 11

C3b

Question 12

Is the alternative pathway innate or adaptive?

Answer 12

innate

Question 13

What do all pathways of the complement cascade result in?

Answer 13

C3 convertase enzyme and the formation of the membrane attack complex

Question 14

Why is complement fixation by the classical pathway not occuring in the blood stream even though the antibody and complement components are circulating together?

Answer 14

the C1 binding site is not available becauase the antibody is not bound to the antigen; no conformationial change to the antigen to allow for binding

Question 15

What are the classes of antibody that can fix complement?

Answer 15

IgM and IgG

Question 16

Which antibody is most efficient at fixing complement and why?

Answer 16

IgM; because only IgM molecule is required to activate the complement, two IgG molecules are required to activate complement

Question 17

What is the membrane attack complex?

Answer 17

a structure that is assembled in membranes after the activation of the complement cascade; hydrophilic on the inside and hydrophobic on the outside

Question 18

What is the membrane attack complex composed of?

Answer 18

predominantly of 10 to 16 molecules of C9 that forms a barrel shaped pore

Question 19

What does the membrane attack complex do?

Answer 19

it punches a hole in the target membrane so that it can directly lyse and kill the microbe

Question 20

Why is the alternative complement pathway not initiated in mammalian cells but it is in bacterial cells?

Answer 20

because mammalian cells have protective mechanisms that inactivate C3b, bacteria do not

Question 21

What are the four ways that complement can contribute to eliminating bacteria?

Answer 21

opsonization, increased vascular permeability, anaphylatoxins, neutrophil chemotaxis

Question 22

What molecules are involved in opsonization?

Answer 22

C3b and the antibody IgG

Question 23

What is opsonization?

Answer 23

the coating of bacteria which makes it easier for phagocytic cells to attach to and phagocytize the bacteria

Question 24

What molecules are involved in increased vascular permeability?

Answer 24

C2a, C3, and C5a

Question 25

What do the molecules involved in increased vascular permeability allow for in the blood vessel?

Answer 25

they allow neutrophils, macrophages, and lymphocytes to exit the blood vessel easier and enter the tissues

Question 26

What molecules are involved in anaphylatoxins?

Answer 26

C3a and C5a

Question 27

What do anaphylatoxins cause?

Answer 27

mast cell degeneration

Question 28

What does mast cell degeneration cause?

Answer 28

an increase in vascular permeability and vasodilation and allow defenses to get to the site of infection

Question 29

What class of antibodies sensitizes the cell?

Answer 29

IgE

Question 30

What molecules are involved in neutrophil chemotaxis?

Answer 30

C5a

Question 31

What does neutrophil chemotaxis cause?

Answer 31

neutrophils to go to the area where bacteria are located and stimulates their killing mechanisms

Question 32

Where are the important molecules involved in regulating the complement system located?

Answer 32

soluble proteins freely flowing in blood, and membrane bound molecules

Question 33

What two ways the complement system can be inactivated in a blood sample?

Answer 33

heating it to 56 degrees celcius for 30 minutes, and chelating Ca and Mg with EDTA