1-28 Generation of Diversity of B and T cells

Question 1

naive b-cells express..

Answer 1

a membrane bound IgM B-Cell receptor

Question 2

when naive b-cells encounter antigen, they

Answer 2

become activated and prolifterate into plasma cells that secrete IgM antibody in both secreted and membrane bound forms

Question 3

How do activated b-cells co-express surface and membrane bound immunoglobulin?

Answer 3

occurs due to differential mRNA processing

starting at 5’ end, the variable coding region (VDJ) followed by IgM region and then IgD region

to produce membrane bound, hydrophilic section cut out and constant region is attached directly to hydrophobic region

to produce excreted form, hydrophobic section cut out, hydrophilic attached directly to constant region

Question 4

co-expression of BCR Ig and secreted Ig does not require ____ ________

Answer 4

DNA rearrangement

Question 5

describe immunoglobulin class switching

Answer 5

there are “Switch regions” between the various Ig motifs following the VDJ sequence. The enzyme AID nicks the DNA at these switch regions, and another enzyme brings these nicked regions together and repairs them, looping out intevening DNA. when transcription begins, one of the different Ig motifs will occur just after the variable region

Question 6

after a b-cell encounters its specific antigen

Answer 6

its begins to tailor the antibodies it produces to the type of protection needed
IgE - allergies
IgA - secretory
IgG - various functions

Question 7

class switch occurs at the _____ level

Answer 7

DNA

Question 8

which mRNA of the immunoglobulin determines if it is secreted or membrane bound?

Answer 8

the Fc (constant) region of the heavy chain

Question 9

how do you get so much B-Cell diversity?

Answer 9

Immunoglobulin gene consists of segments of DNA that can be mixed and matched

immunoglobulin genes have different segments, b-cell can pick one of each (lambda light chain locus, kappa light chain locus, heavy chain locus)

Question 10

light chains have

Answer 10

V and J regions which are randomly chosen

Question 11

HEavy Chains have

Answer 11

V, D, and J regions which are randomly chosen

Question 12

The b cell combines

Answer 12

the light and heavy chains

Question 13

the constant region - all start as

Answer 13

IgM

Question 14

what flanks the V and J;s?

Answer 14

signal sequences that are recognized by enzymes that pull them together. these signal sequences work in such as way that they allow enzymes to work and cause recombination of the heavy chain or light chain loci

Question 15

what enzymes are involved in this recombination?

Answer 15

RAG1 and RAG2.

Question 16

what happnes if you are missing Rag1 or Rag 2?

Answer 16

severe combined immunodeficiency - cant rearrange the DNA in B or T cells.

Question 17

describe the role of RAG

Answer 17

brings together sequences in a way that they are subject to splicing. Ligase comes and glues them together.

DNA is spliced, not the RNA, removing a “loop” of intervening DNA which is lost.

Question 18

regions get added during

Answer 18

splicing. N and P regions
P regions are palendromic regions
N regions are truly variable

Question 19

TDT

Answer 19

the two ends of clipped DNA get close, clip gets made, each end overhangs. TDT (terminal dexoydase transferase) adds random nucleotides to ends of DNA. Repair enzyme then does base matching to fill in

Question 20

person lacking TDT?

Answer 20

makes antibody, makes t-cell receptors, but b-cells have low affinicty and t-cells dont react as well. Can’t create the random sequences that by chance have high affinity

Question 21

more N regions in the heavy or light chains? why?

Answer 21

more in heavy chains because there is more TDT around during heavy chain rearrangment

Question 22

most recombinations will….

Answer 22

fail to make a complete protein.

if you get out of reading frame, the contant region will not work.

2/3 rearrangements are out of reading frame.

Question 23

describe chain rearrangement steps

Answer 23

1. heavy - D-J rearrangements on both chromosomes of early pro-b cell
2. heavy - VDJ rearrangements on first chromosome, if fails, try second chromosome, if fails, apoptosis
3. light - if successful, kappa gene on first chromosome of light chain rearrangemnts, if fails, try second chromosome, if fails, lambda gene on first chromsoome, if fails, lambda gene on second chromsome, if fails, apoptosis
4. light - if kapppa rearrangement successful - expresses mu and kappa(light chains) on (IgM)
5. light - if lambda rearrangement successful and not kappa, expresses mu and lambda (light chains) on IgM

Question 24

how does a cell determine if a heavy chain works?

Answer 24

create a “fake” or surrogate light chain, ssee if the heavy chain folds properly. If it can’t make ti to the surface or act properly with the light chain, apoptosis.

Question 25

difference between light and heavy chain rearrangement?

Answer 25

each light chain chromosome gets 2 opportunitues (4 total) to rearrange. Each heavy chain chromosome gets 1 opportunity (2 total) to rearrange.

Question 26

if the first time a light chain rearranges,…

Answer 26

great. but if not, it can keep taking different V and J sections from further down the chromosome until it runs out of time or runs out of dna OR successfully makes a V-J recombination.

Question 27

how do rearrangements get selected on for increased affinity?

Answer 27

• cell commits to b cell lineage
• generates heavy chain diversity in pro-b population
• selectes for functional heavy chains, all other apoptosis
• generates light chain gene diversity in pre-b cell population
• selects for functional light chains
• b cells making functional IgM selected for.

only those that make the functional IgM survive.

Question 28

prescence of RAD during rearrangment?

Answer 28

early on, burst of rad when rearranging heavy chain, then another burst later when rearranging light chain

Question 29

when are surrogates made?

Answer 29

only after rearrangement of the heavy chains and UNTIL we are ready to rearrange the light chains. After heavy, before light.

Question 30

when is TDT mostly present?

Answer 30

during the entire rearrangement of heavy chain, but fades as light chain rearranges.

Light chain shave less N regions made by TDT than heavy chains that have TDT present the whole time.

Question 31

splicing can occur either way, creating ______ depending on

Answer 31

creating secreted or membrane bound, depending on cell signals

Question 32

IgM and IgD splice type?

Answer 32

RNA splice

Question 33

IgG, IgE, and IgA splice type?

Answer 33

DNA splcie

Question 34

the process of t-cell and b-cell process is the same except for

Answer 34

mutations of b-cells occur during immune response across the whole variable region of the DNA. Single bases randomly mutated. localized to variable region.

Question 35

purpose of somatic hypermutations?

Answer 35

happens to B-Cells when T-cells are stimulated, provides more diversity to fight infection

Question 36

why are the mutations lined up in the hypervariable region?

Answer 36

Early on – mutations occur, but only few

As immune response matures and class switch, more and more mutations

Why lined up in hydrvaerribale region? If they make the antibody not bind to antigen anymore, cell doesn’t get stimulated – cell apoptosis
IF they make the antigen that binds to the antibody (bcell) better, will divide and get stimulated more.

Question 37

AID is responsible for

Answer 37

both class switching AND somatic hypermutation

Question 38

if a person has a dieases where t-cells dont stimulate b-cells properly

Answer 38

they would have no class switching and they would have low affinity antibodies becasue they didnt get antibody affinity maturation

Question 39

there are antigens that are t-cell independant, describe.

Answer 39

stimulate b cells but not t-cells. (bacterial liposaccharides, because t-cells see protein) – you get IgM and no memory (wont get the Things that t-cells do)

Question 40

without t-cell help..

Answer 40

Without t-cell help  no AID  no class switching or hypermutation

Question 41

t-cells do not ____

Answer 41

class switch or mutate - T-cells are highly educated at self vs non-self. We do’t want a t-cell to start getting mutations in t-cell receptor after being selected for not attatcking self.

Question 42

T-cell receptor look slike _____ and has two classes

Answer 42

looks like a b cell receptor, alpha-beta and gamma-delta

Question 43

differences/similarities between b cell and t- cell diversity generation?

Answer 43

Is a mirror of the immunoglobulin molecule in terms of how it gets its varibalilty. Everything with RAg1 and 2, splicing, and addition of TDT to make N-regions which give more diversity to binding sties. Everything is the same in a t-cell as it is in a b-cell. Isntead of heavy then light, its beta then alpha chain

Question 44

when is a b cell a b cell? when is a t-cell a t-cell?

what machinery makes this happen?

Answer 44

Until cell puts IgM on surface, not a b cell
Until a cell puts T cell receptor on surface, not a T-cell

Without RAG1 and RAG2, and protein kinases for splicing, you do not get B cells or T-Cells.

Question 45

where does somatic hypermutation occur?

Answer 45

B-Cells only!

Question 46

T-cells and b-cells use essentially the same mechanisms to

Answer 46

rearrange their antigen receptors