Lecture 6

Question 1

Where do T cells develop and mature?

Answer 1

• develop in the bone marrow
• mature in the thymus

Question 2

Where do B cells develop and mature?

Answer 2

develop AND mature in the bone marrow

Question 3

What is an antigen?

Answer 3

• a macromolecule (protein, polysaccharide, glycoproteins)
• recognized by the body as foreign
• stimulates an immune response
• can be foreign or self

Question 4

What is an epitope?

Answer 4

region or site of antigen that are recognized by the immune system (they bind to Igs or TCRs)

Question 5

What are B cell receptors also known as?

Answer 5

Immunoglobulins (antibodies)

Question 6

What is the membrane-bound form of the B-cell receptor called and what is it bound to?

Answer 6

BCR; bound on the B-cell surface

Question 7

What is the secreted form of B-cell receptors called? Where do they bind pathogens?

Answer 7

antibody; in the extracellular spaces

Question 8

What is the structure of an antibody?

Answer 8

• Y-shaped
• Two hinged heavy chains
• Two light chains

Question 9

What joins the chains in an antibody together?

Answer 9

disulphide bonds

Question 10

What is avidity?

Answer 10

The total strength of the interaction between an antibody and an antigen

Question 11

What is affinity?

Answer 11

The strength of the interaction between a single antigen-binding site and antigen

Question 12

What are the two types of immunoglobulin domains in an antibody?

Answer 12

variable and constant

Question 13

What do the variable regions of immunoglobulins determine?

Answer 13

antigen-binding specificity

Question 14

What do the constant immunoglobulin domains of an antibody determine?

Answer 14

the different Ig classes: ie: IgM, IgG, IgD, IgA, IgE

Question 15

What is the hinge region of an antibody?

Answer 15

• lies within the C region
• allows flexibility in binding multiple antigens
• differs between isotypes

Question 16

What are distinct characteristics in the C region?

Answer 16

1. number and location of disulphide bonds
2. number of attached carb groups
3. number of C domains
4. length of hinge regions

Question 17

How many subclasses of IgG exist? List them in decreasing order

Answer 17

IgG1, IgG2, IgG3, IgG4

Question 18

How many subclasses of IgA exist?

Answer 18

2; IgA1, IgA2

Question 19

What is the most abundant Ig in serum?

Answer 19

IgG

Question 20

What is the first Ig produced after B-cell activation?

Answer 20

IgM

Question 21

In what form is IgM secreted and where?

Answer 21

pentamer; normally in bloodstream but not in tissues

Question 22

Which Igs activate the classical pathway of complement?

Answer 22

most IgGs and IgM; IgA, IgG and IgD do not activate complement

Question 23

Which Ig is the heaviest?

Answer 23

IgM

Question 24

Where and how does IgA act?

Answer 24

at mucosal surfaces; secreted into gut and respiratory tract and breast milk

Question 25

What does IgE do?

Answer 25

acts in parasite immunity and allergic reactions; high-affinity binding to mast cells and basophils

Question 26

What does IgD do?

Answer 26

has an unknown role; present on the surface of mature B cells as a marker

Question 27

What Ig participates in placental transfer?

Answer 27

IgG

Question 28

How do the IgM and IgA molecules form polymers?

Answer 28

by interacting with the J chain

Question 29

How many antigen-binding sites do IgM molecules in plasma have

Answer 29

10

Question 30

IgA is found as ____ in mucous secretion but as ____ in plasma

Answer 30

dimers; monomers

Question 31

____ are regions within the variable regions of H and L chains

Answer 31

hypervariable regions

Question 32

Do the hypervariable regions of antibodies directly or indirectly make contact with the antigen?

Answer 32

- directly - actually contact the antigen - makeup the antigen-binding site - also called complementarity-determining regions

Question 33

How many hypervariable regions are there? What are their names?

Answer 33

3; HV1, HV2, HV3

Question 34

Where is the most variable part of the domain?

Answer 34

HV3

Question 35

What are the regions between hypervariable regions called? How many are there?

Answer 35

framework regions; 4 (FR1-FR4)

Question 36

The immune system generates antibodies of different specificities. How does it do this?

Answer 36

- by creating various combinations of H-chain and L-chain V regions - process known as combinatorial diversity - formation of VH and VL region genes from smaller DNA segments

Question 37

When does combinatorial diversity occur?

Answer 37

during development of B cells in the bone marrow

Question 38

What is the general structure / characteristics of a T-cell Receptor?

Answer 38

- Transmembrane proteins with an almost entirely extracellular structure - two protein chains (a and B) - each chain has C and V region - V region of a and B chains make the antigen-binding site - Each T cell expresses one type of TCR which can offer protection against only one pathogen

Question 39

Most TCRs can only recognize ____

Answer 39

small peptides

Question 40

Peptides must be presented via cell-surface receptors called ____ to T cells

Answer 40

MHC / HLA family

Question 41

How do the structures of MHC class I and MHC class II differ?

Answer 41

**MHC class I **: - three alpha subunits and a beta macroglobulin - alpha 1 and 2 form the peptide-binding groove - alpha 3 is the only subunit that anchors MHC to the plasma membrane **MHC class II** - two alpha and two beta subunits - alpha 1 and beta 1 form the peptide-binding groove - alpha 2 and beta 2 anchor MHC to the plasma membrane

Question 42

the MHC presenting the antigen binds to both the ____ and the ____

Answer 42

TCR and a co-receptor expressed on the T-cell surface

Question 43

What are the two co-receptors of T cells? What MHC do they bind to and do they target extracellular or intracellular pathogens?

Answer 43

1. CD4: binds MHC-II, targets EXTRACELLULAR pathogens 2. CD8: binds to MHC-I, targets INTRACELLULAR pathogens

Question 44

TCR is not expressed without ____ because:

Answer 44

CD3; it is required to bring TCR to surface

Question 45

What does the CD3 complex do?

Answer 45

Recruits the signaling molecules that are activated upon TCR engagment which drives T cell activation