Pharm lecture 7 - antibodie

Question 0

What is the FAB region?

Answer 0

antigen binding region of antibodies. variable regions of heavy and light chains

Question 1

What is the structure of antibodies?

Answer 1

2 heavy chains and 2 light chains

Question 2

What is the FC region?

Answer 2

Constant region of heavy chain - immune effector region

Question 3

What are the types of IgG?

Answer 3

IgG1, IgG2, IgG3, IgG4

Question 4

What type of antibody are therapeutic antibodies?

Answer 4

IgG

Question 5

What are the characteristics of monoclonal antibodies? (4)

Answer 5

1) Homogenous for antibody type, amino acid sequence, affinity and specificity
2) High specificity
3) High Affinity
4) long half life in vivo

Question 6

What are the following characteristics for an antibody administered subcutaneously or intramuscularly?

Bioavailability?
time till peak concentration?

Answer 6

Bioavailability: 24-95%

time till peak concentration: 7-8 days

Question 7

What are 4 types of monoclonal antibodies and their suffix?

Answer 7

Murine: -o
Chimeric: -xi
Humanized: -zu
Human: -u

Question 8

How are antibodies administrated subcutaneously or intramuscularly absorbed? What is this route of administration limited by?

Answer 8

Absorbed slowly by convective absorption through lymph vessels and by diffusion into blood vessels

Limited by volume that can be injected at these sites

Question 9

Where are antibodies distributed? (3)

Answer 9

Extra-cellular distribution

Access restricted across diffusional barriers unless transport is facilitated

Does not cross blood brain barrier so does not enter CNS

Question 10

What is the function of the Neonatal Fc receptor? (FcRn) (2)

Answer 10

1) Transfers passive immunity across placenta from mother to fetus (IgG antibody)
2) Protects IgG from degradation, prolonging half life in serum

Question 11

What cells express the Neonatal Fc receptor? (5)

Answer 11

Hepatocytes
endothelial cells
phagocytic cells
APC
intestinal epithelium

Question 12

How does FcRn protect IgG from degradation? (3 steps)

Answer 12

1) IgG undergoes endocytosis into low pH endosomes promoting IgG binding to FcRn (because FcRn only binds IgG at acidic p.H.)
2) FcRn-IgG complex resistant to lysosomal enzymatic degradation - free IgG is degraded
3) GcRn-bound IgG is returned to cell surface where it dissociates at physiological p.H.

Question 13

What are the half lives for the isotypes of IgG?

Answer 13

IgG1, IgG2, IgG4 = 20-21 days half life

IgG3 = 7 days half life

Question 14

Why does IgG3 have the lowest half life?

Answer 14

Because it has a single amino acid difference so that it does not bind FcRn

Question 15

How long is the Murine mAB half life in humans and why?

Answer 15

12-48 hours because it does not bind with FcRn

Question 16

What is the half life of antibody fragments and why?

Answer 16

11-27 hours - lack Fc region so does not bind FcRn

Question 17

What are the mechanisms resulting from antigen-antibody binding?

Answer 17

1) Antagonism/neutralization
2) Cell signaling inhibition
3) Antibody dependent cellular cytotoxicity (ADCC)
4) Complement-dependent cytotoxicity (CDC)
5) Selective delivery of toxins or radionuclides
6) Selective imaging

Question 18

What is antagonism or neutralization?

Answer 18

Antibody acts as a competitive inhibitor blocking interaction of a soluble antigen with its ligand, thus decreasing the concentration of unbound soluble antigen in plasma

Question 19

What is Cell signaling inhibition?

Answer 19

Antibody binds cell surface signaling molecule such as a receptor or adhesion molecule to inhibit cell activation or a signaling function.

Can inactivate a pathway or activate a pathway and can act as an agonist or competitive inhibitor

can promote ADCC

Question 20

What is Anti-body dependent cellular cytotoxicity (ADCC)?

Answer 20

Antigen-bound antibody induces lysis of a target cell by an activated NK cell, neutrophl or macrophage

Question 21

Which antibodies show the greatest activity for ADCC?

Answer 21

IgG1 and IgG3

Question 22

How does an antibody cause ADCC?

Answer 22

1) Fab region binds cell surface protein on target cell
2) Fc region binds Fc receptor on NK cell or macrophages
3) NK cell releases cytotoxins or macrophage phagocytoses target cell

Question 23

What is complement-dependent cytotoxicity?

Answer 23

Antigen-bound antibody induces lysis of a target cell by activation of the complement system

Question 24

What is the mechanism of compliment-dependent cytotoxicity (CDC)?

Answer 24

1) Fab region binds a cell surface protein on the target cell
2) Fc region binds complement protein C1q and activates the complement system resulting in cell lysis

Question 25

What is the mechanism of the selective delivery of toxins or radionuclides by antibodies? (3 steps)

Answer 25

1) toxins or radionuclides are conjugated to an antibody
2) antibody binds to cell surface protein of target cell and selectively delivers the toxin or radionuclid
3) antibody-toxin complex is internalized and toxin or radionuclid released to kill target cell

Question 26

How are antibodies used for selective imaging?

Answer 26

1) Radiocontrast agent or radionuclides are conjugated to antibody
2) Antibody binds to cell surface protein on target cell and delivers imaging agent
3) Radiocontrast agent or radionuclid detected or imaged

Question 27

What is immunogenicity?

Answer 27

Antibodies are foreign proteins so they can promote generation of endogenous antibodies against the therapeutic antibody

Question 29

What are the factors that influence immunogenicity?

Answer 29

1) Fraction of foreign amino acid sequence in antibody (high for murine, low for human)
2) Increases with duration of therapy
3) More frequent with low doses
4) More likely with subcutaneous then intravenously