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Immunology 7070 > Lecture 6 > Flashcards

Lecture 6 Flashcards

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1
Q

List the potential functions/roles of Ig

A 
Neutralization
Opsonization
ADCC
Complement
Mucosal Immunity
Immune evasion
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2
Q

What is X gammaglobulinemia?

A

XLA is an x-linked trait where the person cannot create mature B cells and therefore no antibodies. These people can get very sick.

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3
Q

What happens when you subject an IgG to papain?

A

You get a separation of the Fab and the Fc portions.

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4
Q

What happens when you subject an IgG to pepsin?

A

It degrades a portion of the Fc and you are left with the pFc’ and the F(ab’)2.

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5
Q

What is the definition of antibody affinity?

A

The strength of the binding between antibody binding site and a single epitope.

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6
Q

What is the definition of antibody avidity?

A

The number of binding sites on the antibody and their ability to react with multiple epitopes.

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7
Q

List the antibody isotypes.

A

IgA, IgD, IgE, IgG, and IgM

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8
Q

What are the functions of IgG?

A 
Neutralization
Opsinization
Classical complement pathway activation
ADCC
Passive immunity
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9
Q

What are the functions of IgM?

A

Pentamer activation of the classical complement pathway

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10
Q

What are the functions of IgA?

A

Mucosal immunity

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11
Q

What are the functions of IgE?

A

Mast cell degranulation and parasite killing by eosinophls

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12
Q

How do antibodies neutralize toxins? Give an example.

A

They bind to the toxin preventing it from interacting with receptors on host cells.
E.g. Tetani botulinum toxin

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13
Q

How do antibodies neutralize microbes from cell entry?

A

Antibodies adhere to the microbe’s cell surface epitopes blocking the binding with the host’s cell surface receptors.

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14
Q

Give a scenario in which antibodies can block re-infection.

A

If a cell is infected the microbes can sometimes spread to nearby cells. Antibodies are able to neutralize the microbe once it exits the originally infected host cell to spread to the next and block it before entry.

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15
Q

Give an example of an antibody that is able to bind a protein but not neutralize it.

A

GP120 from HIV is able to be bound but it does not neutralize HIV nor stop the virus from infecting.

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16
Q

What is the difference between binding and neutralization of antibodies?

A

Binding of antibodies only means that the antibody can recognize the epitope. Neutralization requires that the epitope is no longer able to function.

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17
Q

How can we detect antibody functions?

A

ELISA

Virus neutralization assay

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18
Q

Define opsonization.

A

The biding of antibodies to microbe surfaces to promote ingestion by phagocytes.

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19
Q

What effect can a splenectomy have on infection rates? Why?

A

Rates of infection (esp by encapsulated bacteria) sans spleen go up because the spleen contains phagocytes and is where phagocytic clearance of opsinized bacteria takes place.

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20
Q

What is the most powerful binding tool recognized by a phagocyte for opsonization?

A

If antibodies AND complement C3b are coating the bacterium the phagocyte can recognize the bacterium much better

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21
Q

What are the steps for opsonization of a microbe and the killing of the same?

A 
Opsonization of microbe by IgG
Binding of opsonized microbes to phagocyte Fc receptors (FcgammaRI)
Fc receptor signals activate phagocyte
Phagocytosis
Killing of ingested microbe
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22
Q

What are the Fc receptors called?
Where are they located?
What are they used for?

A

FcgammaRI
Macrophages, neutrophils, and eosinophils
Ab recognition and phagocytosis

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23
Q

How many Fc receptors are there? Name them.

A 
4.
FcgammaRI IA
FcgammaRI IB
FcgammaRI IIA
FcepsilonRI
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24
Q 
What are the functions of:
FcgammaRI IA
FcgammaRI IB
FcgammaRI IIA
FcepsilonRI
A

Phagocytosis
feedback inhibition on B cells
ADCC by NK cells
Cell activation by Mast cells, basophils, and eosinophils

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25
Describe in brief ADCC
When an opsonized microbe activates an NK cell via Fcgamma RIII to cause cytotoxic killing
26
Briefly describe the IgE mediated killing of parasites
IgE binds to epitopes on helminths which binds to eosinophil FcepisolonRI with high affinity causing the killing of the helminth
27
How can complement pathways become activated/
Alternatively Classically Mannose binding Lectin
28
Describe complement proteins in brief.
A collection of proteins that are a part of the humoral innate immune system that have mechanisms of self and non-self discrimination. These proteins go through a sequential process of proteolytic cleavage causing the elimination of microbes.
29
Describe the complement protein sequences following activation by the alternative pathway
Microbe directly activates the cleavage of C3 leading to C3a&b Formation of C3 convertase with C3b Cleavage of new C3 Covalent binding of new C3b to microbial surface along with C5 convertase Late steps of complement activation
30
Describe the complement protein sequences following activation by the classical pathway
IgG antibody recognizes the microbe and C1 recognizes the IgG on the microbe. Formation of C3 convertase Cleavage of C3 Covalent binding of new C3b (to microbial surface and IgG on surface) along with C5 convertase Late steps of complement activation
31
Describe the complement protein sequences following activation by the mannose binding lectin pathway
Lectin binds mannose on the surface of a microbe. Formation of C3 convertase Cleavage of C3 Covalent binding of new C3b to microbial surface along with C5 convertase Late steps of complement activation
32
What is the function of complement protein C3a?
stimulates inflammation
33
What components make up the C3 convertase in the alternative pathway?
C3bBb complex
34
What factor cleaves factor B in the complement alternative pathways?
Factor D plasma serine protease
35
What component stabilizes the C3bBb convertase?
Properdin
36
What components make up the C5 convertase in the alternative pathway?
C3bBbC3b
37
What components make up the C3 convertase in the classical pathway?
C4b2a
38
What components make up the C5 convertase in the classical pathway?
C4b2aC3b
39
How is the MAC complex initiated?
C5C5b protein
40
What is the function of C7 complement protein?
inserts MAC into lipid membranes
41
What is the function of C8 complement protein?
Initiates binding and polymerization of C9
42
What is the function of C9 complement protein?
Polymerizes to form membrane pores
43
What are the functions of the complement system?
Microbe elimination during immune responses Opsinization Direct microbe killing Chemotactic attraction Processing of immune complexes Augmentation of localization of antigen to B cells and APCs
44
How do complement proteins mediate phagocytosis (in brief).
Binding of C3b or C4b to microbe (opsinization) Recognition by receptor CR1 Phagocytosis
45
Briefly describe the steps (REALLY briefly - 3 steps) to complement mediated cytolysis.
Binding of C3b to microbe Formation of the MAC Osmotic lysis of microbe
46
Briefly describe how complement proteins stimulate inflammatory reactions.
Proteolysis of C3, C4, and C5 to release the a portions Recruitment and activation of leukocytes by a portions Destruction of microbes by leukocytes
47
What roles do C3 complement proteins fill in processing immune complexes?
Reduction in lattice size of Ig Binds to RBCs CR1 and transport to mononuclear phagocyte system Uptake by mononuclear cells and degradation of Ag Localization to B cell, DCs, and APCs
48
Briefly describe the deficiencies in complement proteins in people and their consequences.
C3 deficiency - susceptible to infections. If early in life = fatal. C2/C4 deficiency - normal. Other pathways can be used. C9 (MAC) deficiency - increased Neisseria infections
49
What do the consequences of C2/C4 deficiencies tell us about the functions of C2/C4 complement proteins?
Since deficient people are normal then the functions of these proteins must be redundant and other proteins are able to pick up the slack.
50
Why are complement proteins regulated?
If uncontrolled they can be harmful by causing increased activation and cytotoxicity.
51
How can host cells regulate complement protein activation?
They display regulatory proteins.
52
List host cell regulatory proteins for the complement system.
DAF - decay accelerating factor MCP - membrane co-factor protein CR1 - type 1 complement receptor
53
How do complement regulating proteins DAF, MCP, and CR1 execute their functions?
DAF and CR1 cleave Bb from C3b. | MCP and CR1 mediate further cleavage of C3b into unusable form.
54
Why is it important to heat the sample sera before analysis via virus neutralization assay?
To destroy complement activity
55
What would happen if someone were deficient in C1 inhibitor?
They would get hereditary angioneurotic edema due to over C1 activation
56
What would happen if someone were deficient in glycolipid anchor synthesis?
DAF and MCP would also become deficient and the complement system would run wild destroying erythrocytes
57
Briefly describe mucosal immunity
IgA is at the mucosal surface (first line of defense) and can be actively transported to and secreted from mucosal surfaces.
58
How can IgA be transported to the lamina propria?
By poly-Ig receptor on the basal surface of epithelial cells. There it is endocytosed and secreted into the lumen where the poly-Ig receptor is cleaved by a protease
59
Briefly describe neonatal immunity.
Maternal antibodies are transported across the placenta in a process called passive immunity. Some animals, like cattle, do the same in the milk as their antibodies do not cross the placenta membrane
60
How can maternal antibodies in the fetus/baby affect the baby's immune system?
Maternal antibodies can help inhibit the immune responses that a baby might have to vaccines.
61
Briefly describe how microbes are able to evade the humoral immune system.
Antigenic variation Inhibition of complement activation Microbe proteins binding FC of Abs Resistance to phagocytosis
62
What regions of antibodies are involved in the functions of antibodies?
The Fab portion is the binding site of the antibodies to the epitopes. Fc portions of antibodies are involved with the recognition of leukocytes and other receptors for opsonization.
63
How do heavy chain class switching and affinity maturation improve the abilities of antibodies to combat infectious pathogens?
They aid in the constant variation and change in epitope recognition and allow the antibodies to bind to new threats more efficiently.
64
Why does the complement system not react against host cells and tissues?
Read on this
65
What components of the complement system mediate opsonization?
C3b, C4b and CR1
66
What components of the complement system mediate MAC?
C9
67
What components of the complement system mediate chemotaxis?
C3a, C4a, and C5a
68
How do antibodies prevent infections by ingested and inhaled microbes?
They can bind to the microbes outside and neutralize them
69
How do neonatal animals develop the capacity to protect themselves from infections even before their immune systems have reached maturity?
Passive immunity through placenta or the breast milk
70
Why are there so many numerous pathways for Ig function?
Many pathogens can infect and we need to kill by many different ways and there are many redundancies to ensure that we are protected.
71
Describe how pathogens can evade the humoral immune system?
By cleaving complement proteins By evading Ig binding By evading Ig neutralization etc. etc.
72
You treat an IgG monoclonal antibody with a reducing agent. What happens to the antibody?
Reducing agent breaks cysteine bonds (disulfide bonds) that hold the heavy and light chains together so the four parts will come apart.
73
How can you make antibodies that have dual specificity?
Use a reducing agent to cleave the heavy and light chains then take a non-reducing agent and create new antibodies (out of monoclonal). This makes 3 different antibodies. Purify using affinity chromatography. Abs made using allelic exclusion so they only make Abs with the same binding sites.
74
What advantages would duel specificity antibodies have?
They would be able to bind two different Ags and could theoretically bring two cell types together for interaction.
75
Why are duel specificity antibodies not generated by organisms?
Allelic exclusion.

Immunology 7070 (15 decks)

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