Ch.4 Antigen Recognition in the Adaptive Immune System

Question 1

Cross linking

Answer 1

• adjacent antigen receptors bind 2 or more antigens
• brings the signal transduction parts closer together into an aggregate
• phosphorylation and signal transduction

Question 2

Another name for hypervariability region of antigen receptors

Answer 2

complementartity determining regions

Question 3

Signal transduction component of BCR

Answer 3

BCR = antibody + Igalpha, IgBeta

Question 4

signal transduction component of TCR

Answer 4

TCR = receptor for MHC + CD3 and zeta

Question 5

Hv region with most variability?

Answer 5

CDR3 region at junction btw C and V areas

Question 6

Fab

Answer 6

fragment antigen binding region - where the antigen actually binds

Question 7

Fc

Answer 7

Fragment crystalline - conserved region responsible for biological activity and effector functions

Question 8

difference btw kappa and lambda light chain?

Answer 8

they differ in their C(L)region but not in function

Question 9

types of heavy chains

Answer 9

mu, delta, gamma, epsilon, alpha corresponding to IgM, IgD, IgG, IgE, IgA
- they vary in their C regions (not Fc)

Question 10

isotypes (or classes) of heavy chains

Answer 10

IgG v. IgA - different C regions

Question 11

Heavy Chain Class switching

Answer 11

• Naive B-cells (have not been exposed to antigens) express IgM and IgD
• once activated by antigen and T-cells, Some of their progeny B-cells will be of other heavy chain classes
• even though the C-regions change (different classes) the antigen specificity remains the same (same V region)

Question 12

affinity

Answer 12

• strength of bond btw antibody and epitope of antigen

- represented by Kd - smaller Kd = higher affinity

Question 13

Affinity Maturation

Answer 13

• increase of affinity of antibodies with increased exposure to the antigen
• so you get the same disease more than once

Question 14

Avidity

Answer 14

• told strength of multiple Antigen to antibody bonds
• IgA dimer - 4 binding locations
• IgM - pentimer - 10 binding locations

Question 15

TCR’s

Answer 15

• made up of an alpha and beta chain.
• both have a V and C region like antibodies
• V has 3 hv regions - CDR3 most variable
• always bound to T-cell membrane
• alpha and beta work together to recognize MHC and peptide

Question 16

gamma-delta TCR

Answer 16

• recognize both protein and non-protein peptides

- abundant in epithelia

Question 17

TCR signal transducers

Answer 17

CD3 and zeta

- Also TCR’s have either CD4 next to them or CD8 to recognize portions of the MHC

Question 18

IL-7

Answer 18

• produced in stromal cells of bone marrow and thymus
• required for the proliferation and survival of immature lymphocytes
• creates a large number of them which can later be specified and selected for

Question 19

Somatic recombination

Answer 19

• in every B and T cell the germ line genes of the variable region are recombined to create diversity of antigen receptors
• there is a V, D, and J region

Question 20

Combinatorial diversity

Answer 20

• any V region can combine with any D region. Any set of VD regions can combine with any J regions
• can put together any set of three dominos to get many different combination

Question 21

Junctional diversity

Answer 21

• gives you even more diversity
• When the D region is connected to the J region and the DJ is connected to the V region, nucleotides can be added or subtracted. - this can lead to frame shift and lots of diversity
• Picking different kinds of glue to hold the three dominos together
• Exonucleases cut out nucleotides
• TdT can add in random nucleotides
• When there are overhangs, P-nucleotides can be added in.
• this is the hv region CDR3 (where the VDJ come together)

Question 22

V(D)J recombinase

Answer 22

• enzyme that recognizes the DNA sequence at the edges of V,D, and J regions
• brings these regions together randomly picking a V,D, and J
• an exonucleas cuts the DNA and then ligase repairs it making the complete straight VDJ DNA region

Question 23

Pro-B cell

Answer 23

First progenitor from the stem cell - stimulated by IL-7

Question 24

pre-B-cell

Answer 24

after the pro-B-cell

- the mu heavy chain has been added

Question 25

Check point 1 for B-cells

Answer 25

• Pre B cell with heavy chain and fake invariant light chains tested for self - recognition
• selects all B cells with a functional H chaing

Question 26

Allelic exclusion

Answer 26

• after a pre-B-cell passes the heavy chain checkpoint, it shuts of heavy chain recombination on the other parent chromosome/allele
• only expresses one parent allele

Question 27

TCR maturation steps

Answer 27

Pro-t-cell - double neg. proliferate with IL-7

• Pre-T-cell- somatic recomb. of Beta chain, test with alpha
  
  • if work then stop other B, start alpha recomb etc
• Immature Double + T-cell - express both CD8 and CD4 - exposed to self MHC
  
  • if bind weakly to one or the other - survive - positive selection and become single + mature T-cell
  • if bind strongly - apoptosis - negative selection