Immune System Part II

Question 1

what do antibodies do (3 steps)

Answer 1

1. bind to and neutralize a bacterial toxin (also viruses and bacteria)
2. coat the pathogen (opsonization) which promotes phagocytosis
3. activate complement (IgG and IgM)

Question 2

what is the ultimate goal of antibodies

Answer 2

target pathogens and their products for elimination by phagocytes

Question 3

antibodies are:

Answer 3

the secreted form of the B cell receptor and are specific

Question 4

what is the antibody structure

Answer 4

• 2 identical light chains
• 2 identical heavy chains
• each light chain is joined to a heavy chain by a disulfide bond (and noncovalent linkages)
• each light chain/heavy chain is joined to an identical light chain/heavy chain dimer by disulfide bonds

Question 5

what do each light chain and each heavy chain contain

Answer 5

• each light chain contains one variable region and one constant region (of one domain)
• each heavy chain contains on variable region and one constant region (of 3 or 4 domains)

Question 6

Fab fragment:

Answer 6

• fragment antigen binding
• composed of the light chain and part of the heavy chain

Question 7

Fc fragment:

Answer 7

• fragment crystalizable
• a portion of the constant region of the heavy chain

Question 8

what do Fc region of antibodies bind to

Answer 8

Fc receptors on cells, which aids in phagocytosis

Question 9

epitope:

Answer 9

the portion of an antigenic molecule that is bound by an antibody

Question 10

monoclonal:

Answer 10

one B cell and its clones will produce many antibody molecules, all of which will have the same specificity for their own epitope

Question 11

polyclonal response:

Answer 11

there are likely to be multiple monoclonal antibodies generated to a particular antigen, all of the individual responses collectively are a polyclonal response

Question 12

B cells all recognize the same ______ just different ____ on it

Answer 12

1. antigen
2. epitopes

Question 13

complementary determining regions are also called:

Answer 13

hypervariable regions (contain 5 to 10 amino acids)

Question 14

what forms the antigen binding site

Answer 14

the 6 hypervariable (3 on heavy and 3 on light) regions of heavy chain and light chain.

Question 15

steps of generation of B cell antigen recognition diversity, and what do these steps ultimately lead to

Answer 15

1. somatic recombination
2. junctional diversity
3. combinatorial diversity
   - lead to billions of circulating B cells with unique specificity

Question 16

what is somatic recombination

Answer 16

to generate the variable region in a light chain, one V and one J segment are joined. to generate the variable region in a heavy chain, one V, one D, and one J segment are joined. There are multiple V, D, J segments to randomly choose

Question 17

what is junctional diversity

Answer 17

addition of new and random nucleotides at the V and J segments of light chain and D and J segments of heavy chain

Question 18

what is combinatorial diversity

Answer 18

different light chains combine the already generated heavy chain

Question 19

what are B cells expressing when they leave the bone marrow

Answer 19

IgM

Question 20

what happens before B cells leave the bone marrow

Answer 20

they undergo a selection process so that they do not have a strong recognition of self

Question 21

what happens to B cells that do not encounter an antigen

Answer 21

they undergo apoptosis

Question 22

in the bone marrow, in a b cell -

Answer 22

heavy chain is generated first: somatic recombination, junctional diversity, addition of µ constant region. Same heavy chain, but different light chains

Question 23

what are the 5 classes of antibodies

Answer 23

IgG, IgM, IgD, IgA, IgE

Question 24

the first class of antibodies produced during an infection are:

Answer 24

IgM class antibodies

Question 25

when and where does class switching take place

Answer 25

in lymph nodes following B cell activation and with help from T cells

Question 26

what happens when B cells leave the bone marrow

Answer 26

1. they circulate between blood and lymph 2. if they encounter an antigen, they phagocytose that antigen and are considered activated 3. in order to secrete antibody they need T cell help, which takes place in the lymph node 4. a B cell will phagocytose the antigen and present pieces of it to a T helper cell in the context of an MHC molecule

Question 27

what is the germinal centre and what doesn't have one

Answer 27

a specialized microstructure that forms in secondary lymphoid tissues. IgM secreting B cells do not have a germinal centre

Question 28

B cells that enter the germinal centre of a lymph node:

Answer 28

undergo somatic hypermutation, with the purpose of generating antibodies of higher affinity for the antigen

Question 29

affininty maturation:

Answer 29

B cells that display higher affinity

Question 30

what happens to B cells that have affinity maturation:

Answer 30

they are selected for and undergo class switching (isotype switching) with the aid of a T helper cell

Question 31

what happens to the B cells that undergo class switching

Answer 31

some will become plasma cells, some will become memory cells

Question 32

what happens to B cells that do not display higher affinity or no longer recognize antigens at all

Answer 32

apoptosis

Question 33

plasma cells have one job:

Answer 33

to secrete antibodies

Question 34

T cells originate in the ______ and mature in the ______

Answer 34

1. bone marrow 2. thymus

Question 35

T cells enter the thymus as:

Answer 35

double negative cells: do not express CD4 or CD8

Question 36

as T cells proliferate:

Answer 36

they rearrange their T cell receptors. T cells recognize self-antigen are eliminated during this process. T cells that leave the thymus are either CD8 and CD4

Question 37

to become activated, T cells:

Answer 37

must recognize antigen, not directly as B cells do since T cells only recognize antigen presented on the surface of MHC molecules

Question 38

MHC Class I are recognized by: MHC Class II are recognized by:

Answer 38

1. CD8+ cytotoxic T cell receptors 2. CD4+ helper T cell receptors

Question 39

T cells are activated by:

Answer 39

dendritic cells

Question 40

dendritic cells carry:

Answer 40

antigens from sites of infection to secondary lymphoid tissue where they become active and present antigen T cells