B and T cell development

Question 1

What does innate immune system recognize compared to adaptive immune system?

Answer 1

• Innate: patterns of non-self or altered self (PAMPs and DAMPs)
• Adaptive: specific epitopes on antigen that are non-self.

Question 2

Compare innate immune cell receptors to adaptive immune cell receptors.

Answer 2

• Innate: express the SAME set of PRRs.
• Adaptive: B and T are generated with unique antigen specificity.

Question 3

Identify heavy chain, light chain, variable regions, constant regions, transmembrane region on immunoglobulin (B cells) and TCR (T cells).

Answer 3

• B cell: Y shape
• T cell: 2 column shape
• Heavy chain: in Y shape that running from inner branch down the body (symmetrically).
• Light chain: in Y shape outer branches (symmetrically).
• Variable regions: distal region from membrane.
• Constant regions: proximal region from membrane.
• Transmembrane region: region that in direct contact with membrane.

Question 4

What are the special/identifiable features on Ig structures?

Answer 4

• 2 identical light chain.
• 2 identical heavy chain.
• Disulfide bridge (connect upstairs and downstair)
• Carbohydrate added (glycosylated Ig change efficacy, T1/2)
• Constant region
• Variable region has antigen binding site.

Question 5

Compare Fab vs. Fc

Answer 5

• Fab = fragment antigen biding, it binds antigen.
• Fc = fragment crystallizable, it interacts with other cell surface proteins. Act as cell surface receptor.

Question 6

Name 5 classes of Ig and what are their unique features? (hint: hinge regions, dimers, pentamers)

Answer 6

• Classes: G/A/M/E/D
• Hinge regions in D, A, G.
• Non-hinge regions M,E.
• Form dimers: A
• Form pentamers: M

Question 7

What kind of antigens can B cells bind? And in what kind of geometry can they bind?

Answer 7

• Antigens can be proteins, lipids, carbohydrates, nucleic acid DNA.
• Can bind to linear or conformation/discontinuous epitope.

Question 8

What is the unique properties that B cell has that affect how they interact with epitope? (hint: region name)

Answer 8

Hyper-variable (HV) region interacting with antigen, surrounded by Frame Region.
AKA complementarity-determining regions.

Question 9

How many antibody can each B cell produces?

Answer 9

ONE

Question 10

List the step of generation of lymphocyte antigen receptors of Ig.

Answer 10

• Start with heavy chain: D-J combine; V to the DJ; Transcription to make mRNA; Splicing to select only portion needed; Translation to make protein.
• Then with light chain: V-J combine; Transcription to make mRNA; Splicing of mRNA; Translation.

Question 11

How does DJ combine?

Answer 11

• RAG (!!!) cleave heptamer, yield hairpins, open hairpins, nick DNA to create palindromic overhangs (P-nucleotides).
• Add nucleotides randomly to ends of single strands (NOT encoded by the genome).
• Gap filled by TdT (Terminal deoxynucleotidyl transferase).

Question 12

Compare membrane bound Ig to secreted Ig.

Answer 12

• Membrane-bound Ig: Ig alpha and Ig beta serve as B cell receptor. Splicing to remove the region “SC sequence” and join “MC exons” in heavy chain. (Think of M = marriage = stay = membrane bound!)
• Secreted IG: primary transcript is cleaved at polyadenylation site, eliminate MC, keep SC. (Think of S = separate = secreted!)

Question 13

What are the results and consequences of Pre-B cell test (1)?

Answer 13

• Test heavy chain
• Weak signal: cell proliferate and undergo light chain rearrangement (pass!)
• Signal too strong: cell eliminated, reacts with antigens in bone marrow.
• No signal: apoptosis.

Question 14

What are the possible outcome of immature B cell? What step is this in testing B cell functionality and self reactivity?

Answer 14

• Test how BCR (surface expression) functional (step 2)
• Weak signal: cell proliferate and leave bone marrow.
• Signal strong: cell rearrange on light chain.
• Signal too strong: apoptosis.

Question 15

What are the results and consequences of transitional B cell (3)?

Answer 15

• Test BCR reactive to antigens in spleen.
• Weak signal: fully mature resting B cells
• Too strong: apoptosis.

Question 16

Prevalence of antibody (rank their abundance)

Answer 16

G > M > A > E

Question 17

What is changed during class switch recombination?

Answer 17

Constant region portion of heavy chain changed, but variable region portion of heavy chain stay the same.

Question 18

What is the elimination of cells that recognize self-antigens called? (hint: bone marrow vs. spleen)

Answer 18

• Central tolerance in bone marrow.
• Peripheral tolerance in spleen.

Question 19

What happened to immature B cells? Mature B cells? Activated B cells?

Answer 19

• Immature B cells who bound to self-cell surface antigens is removed.
• Mature B cell bound to foreign antigen got activated.
• Activated b cell give rise to plasma cell and memory cells.

Question 20

What is the critical difference in B and T cell receptors?

Answer 20

The way they bind antigen
- TCR can bind a diverse array/antigens.

Question 21

Features of TCR (hint: region, chains)

Answer 21

• 2 variable regions [top run horizontally]
• 2 constant regions [bottom run horizonally]
• Encoded by T-cell a and b (or g and d) chains
• Disulfide bridge.
• 1 antigen binding site
• Never secreted

Question 22

Which TCR is the majority of T cells? ab or gd?

Answer 22

ab by >95%
gd only in ruminants 35%

Question 23

Explain recombination to produce TCR

Answer 23

• DJ, then V
• Rearrange alpha chain and Beta chain (rearrrange DNA)
• Thymic selection: test if TCR recognize antigen

Question 24

What kind of epitopes are recognized by T cells: linear or discontinuous? Naive or processing state?

Answer 24

Linear, in the context of APC. They only recognize antigens/epitopes that already processed.

Question 25

What is MHC? And where do you find them?

Answer 25

- Located on APCs. - MHC 1 is intracellular vs. MHC 2 is extracellular - Both use ER to synthesize MHC molecules to present antigens.

Question 26

What does it mean when "MHC locus is highly polymorphic"?

Answer 26

MHC is highly variable, present varying peptides to T cells.

Question 27

Compare/contrast MHC 1 and 2 structures

Answer 27

- MHC1: 8-10 amino acid long - MHC2: 13-25 amino acid long, more open, no rings.

Question 28

What is anchor residue?

Answer 28

Anchor residues are amino acids that help anchor the peptides to the MHC molecule.

Question 29

What does CD4 binds to? What does CD8 binds to?

Answer 29

CD4 to MHC2 = class 2 restricted ; CD8 to MHC1= class 1 restricted

Question 30

What is the flow of immune system (T cells) in terms of organs?

Answer 30

Start as T cell progenitor from bone marrow, then goes to thymus. Once selected, it goes to periphery (secondary lymphoid organ). They start surveying what antigens being presented.

Question 31

Steps of T cell selection.

Answer 31

- Happened in thymus - Enter through corticomedullary junction cortex. - Move up to cortex as 4(neg)8(neg)TCR(neg) = double negative, then interact with cortical epithelial cell. Then if it's interact with MHC1, it becomes CD8; if it interacts with MHC2, it becomes CD4. This interaction is a positive selection. - Once became, it is committed. - Negative selection: if T cell interact with mTEC that has AIRE in it, T cell undergoes apoptosis because it interact with host antigens. Additional note: immature T cells come in naked, no CD4, no CD 8, no TCR. Once entered thymus, chemokines promote T cell to express TCR, CD4 and CD8. Antigens presented on MHC1 or MHC2 will bind to T cell. If antigen on MHC1 binds, it will bind to T cell with CD8, and down regulate CD4. If antigen on MHC2 binds to T cell with CD4, CD8 will be down regulated. Lastly, self antigens will be released to test T cells. If T cells bind antigens, it will be eliminated.

Question 32

What can TCR recognize?

Answer 32

1 single TCR can recognize a range of related peptides in a context of MHC. Governed by CD3.

Question 33

The components of the T cell receptor complex are:

Answer 33

- The TCR alpha and beta chains - Coreceptor CD4/CD8 - Signaling molecule CD3

Question 34

During B cell development, B cell receptors are tested for self reactivity by _____. (Hint: what happened to heavy chain and light chain).

Answer 34

- PreBCR to test heavy chain giving weak signal allowing B cell survival. - Rearranged light chain given weak signal = B cell survival to move out of bone marrow - Rearranged light chain given strong signal = B cell death

Question 35

Immunoglobin class-switch recombination changes _______ of the antibody.

Answer 35

Functionality. NOT specificity!!

Question 36

During T cell development in the thymus, what events occur to T cell?

Answer 36

- T cell that strongly bind antigens presented by MHC 1 and 2 are eliminated. - T cell that can bind MHC 1 OR 2 are positively selected. - T cell change from expressing both CD4 and CD8 to express only one or the other.