Deck 2: Innate Immunity: the Immediate Response to Infection

Question 1

Explain why a genetic deficiency of C3 leads to a type of immunodeficiency characterized by recurrent and severe infections.

Answer 1

C3 is a key element in the initiation of the complement cascade in all three pathways of complement activation,namely the alternative,lectin,and classical pathways.Its cleavage into C3a and C3b occurs early in the complement cascade.C3a acts as an inflammatory mediator and recruits inflammatory cells to the site of infection.C3b becomes fixed to the pathogen surface and facilitates the opsonization of pathogens by phagocytes and the assembly of complement components for perforation of the pathogen membrane.In the absence of C3,all three pathways of complement activation would be arrested and extracellular pathogens would escape immune detection until adaptive immune mechanisms develop fully many days later.

Question 2

Explain the similarities between membrane cofactor protein,factor H,and complement receptor 1 in terms of their complement control properties.

Answer 2

MCP,factor H,and CR1 all bind to C3b and render it susceptible to proteolytic cleavage by factor I.All three contain complement control protein (CCP)modules and are therefore considered regulators of complement activation (RCA).

Question 3

of the following statements are correct regarding \alpha₂-macroglobulin except _____.

A)it binds covalently to its target via a thioester bond
B)it possesses a bait region to lure its target
C)it undergoes a conformational change that enables it to enshroud the target
D)when bound to its target it is cleared from the circulation by hepatocytes,fibroblasts,and macrophages bearing receptors specific for the complex
E)its target is the membrane-attack complex on human cells.

Answer 3

E

Question 4

Identify the incorrectly paired molecular association.

A)iC3: factor B
B)CR4: iC3b
C)properdin: C3bBb
D)membrane cofactor protein: C3b₂Bb
E)decay-accelerating factor: C3bBb.

Question 5

Although activation of the three different pathways of complement involves different components,the three pathways converge on a common enzymatic reaction referred to as complement fixation.
A.Describe this reaction.
B.Describe the enzyme responsible for this reaction in the alternative pathway.
C.Identify the three effector mechanisms of complement that are enabled by this common pathway.

Question 6

Which of the following does not accurately describe complement components?

A)soluble proteins
B)made by the spleen
C)located in extracellular spaces
D)some function as proteases once activated
E)activated by a cascade of enzymatic reactions.

Question 7

Which of the following polymerizes to form a transmembrane channel that compromises the integrity of cell membranes?

A)C5
B)C6
C)C7
D)C8
E)C9.

Question 8

_____ are soluble complement fragments that mediate localized and systemic inflammatory responses.

A)cryptdins
B)defensins
C)anaphylatoxins
D)selectins
E)C-reactive proteins.

Question 9

Which of the three complement pathways becomes activated soonest after an initial infection?

A)the classical pathway
B)the lectin pathway
C)the alternative pathway.

Question 10

importance of CD59 (also known as protectin)is to _____.

A)promote the speed of complement activation by protecting C3 convertase C3bBb from proteolytic degradation
B)prevent the recruitment of C9
C)dissociate the components of the alternative C3 convertase
D)prevent the attachment of C3b to host cell surfaces
E)inhibit the anchoring of C5b,C6,and C7 to host cell surfaces.

Question 11

the early stages of the alternative pathway of complement activation there are complement control proteins that are soluble (factors H and I)and associated with the cell surface (DAF and MCP).Identify the (i)soluble and (ii)cell surface-associated complement control proteins that operate in the terminal stages of the alternative pathway of complement activation,and describe their activities.

Question 12

Which of the following is the membrane-bound form of C3 convertase of the alternative pathway of complement activation?

A)iC3
B)C3a
C)C3b
D)iC3Bb
E)C3bBb.

Question 13

Review the differences between the three pathways of complement (alternative,lectin,and classical)in terms of how they are activated.
B.Distinguish which pathway(s)are considered part of an adaptive immune response and which are considered part of innate immunity,and say why.

Question 14

Which of the following complement components is an opsonin that binds to complement receptor 1 (CR1)on macrophages?

A)C3b
B)C3a
C)Bb
D)Ba
E)C3bBb.

Question 15

membrane-bound proteins on human cells that dissociate and inactivate alternative C3 convertase to avoid complement activation are _____.

A)factor B and factor H
B)factor H and factor I
C)factor B and factor I
D)decay-accelerating factor and factor H
E)decay-accelerating factor and membrane cofactor protein.

Question 16

plasma proteins that counteract the activity of factor P by inactivating C3 convertase through the cleavage of C3b are _____.

A)factor B and factor H
B)factor H and factor I
C)factor B and factor I
D)decay-accelerating factor and factor H
E)decay-accelerating factor and membrane cofactor protein.

Question 17

Explain how the anaphylatoxins C3a and C5a contribute physiologically to inflammation during complement activation.

Question 18

Explain how the alternative C3 convertase on pathogen cell surfaces is (A)formed and (B)stabilized.

Question 19

is it important to expose the hydrophobic sites of C7 and C8 during the formation of the membrane-attack complex?

Question 20

Explain the steps that take place when a bacterium is opsonized via C3b:CR1 interaction between the bacterium and a resident macrophage in tissues.

Question 21

Damage to tissues triggers a cascade of plasma proteins involving bradykinin and is known as _____.

A)the alternative pathway of complement
B)the coagulation system
C)the kinin system
D)receptor-mediated endocytosis
E)the acute-phase response.

Question 22

ligand for CR3 and CR4 formed by the cleavage of C3b by the combined action of factors H and I is called _____.

A)C3bBb
B)C3a
C)C3b₂Bb
D)iC3b
E)C5b.

Question 23

Which of the following are important in anchoring the membrane-attack complex to the membrane?

A)C3 and C5
B)C5 and C6
C)C6 and C7
D)C7 and C8
E)C8 and C9.

Question 24

Which of the following does not describe the actions of the coagulation system?

A)blood clot formation
B)enhancement of dissemination of microbes into lymphatics and bloodstream
C)decrease in blood loss and fluid into interstitial spaces in tissues
D)release of inflammatory mediators by platelets
E)wound healing.

Question 25

Which of the following does not contain a glycosylphosphatidylinositol (GPI)lipid tail?

A)decay-accelerating factor (DAF)
B)homologous restriction factor (HRF)
C)membrane cofactor protein (MCP)
D)protectin (CD59)
E)all of the above contain a GPI tail.

Question 26

Which of the following does not describe defensins?

A)highly conserved with few variants
B)contain a large proportion of arginine residues
C)contain three intra-chain disulfide bonds
D)amphipathic,with hydrophobic and hydrophilic regions
E)disrupt pathogen membranes by penetrating them and disrupting their integrity.
ANSWERS