Antigen receptors and Lymphocyte development

Question 1

What is an antigen?

Answer 1

A molecule which specifically binds a T-cell receptor or an antibody (Ab) site

Question 2

What is an immunogen?

Answer 2

Any molecule that elicits an immune response by binding to a T-cell receptor an antibody

Question 3

Are all antigens immunogens?

Answer 3

No

Question 4

Are all immunogens antigens?

Answer 4

Yes

Question 5

What is the order, lowest to highest of immunogencitiy?

Answer 5

Amino acids
Haptens
Lipids
Steroids
Carbs
Proteins

Question 6

What is a hapten?

Answer 6

Low molecular weight molecules which can never elicit an immune response on its own unless coupled with another molecule

Question 7

What is an epitope?

Answer 7

Antigenic determinant

They are the region of an antigen which can be recognized and bound by a receptor (TCR, BCR)

Question 8

What are the preformed receptors?

Answer 8

PRR (Pattern recognition receptors) and TLR (Toll-like receptors)
KAR (Killer activation receptors) and KIR (Killer inhibition receptors) on NK cells
CR (complement receptors)
FcR on phagocytes

Question 9

What the generated receptors?

Answer 9

T cell receptors (TCR)

B cell receptors (BCR)

Question 10

Describe the structure of a BCR:

Answer 10

Have heavy and light chain with variable and constant regions
Contain co-receptors Ig-Beta and Ig-Alpha
Secreted immunoglobulins are very similarly shaped; they have an Fc portion, an ag binding portion, and a complement binding portion (side of base of Y)

Question 11

What do Ig-Beta and Ig-Alpha do?

Answer 11

NOT INVOLVED IN BINDING
They act as signal transduction molecules that tell the B well when the antigen is bound and transmit a signal to the nucleus to up/down regulate certain actions

Question 12

Describe the structure of a TCR:

Answer 12

Have an alpha and beta chain (95%)
Extracellular portion consists of a variable (V) region, a constant (C) region, and a hinge (H) portion so that it can move a bit during binding
Also has a transmembrane region and short cytoplasmic tails
CD3 portion

Question 13

What does the CD3 portion of a TCR do?

Answer 13

NOT INVOLVED IN BINDING

 It starts the signal cascade to the nucleus and includes the ζ portions (zeta)

Question 14

What is allelic exclusion?

Answer 14

Start with one chromosome (either maternal or paternal) and the other maintains the germ line sequence
Normally it just makes a heavy chain for the B cell
If it messes up and the receptor is not coming out right, we go on to our back up chromosome

Question 15

How much specificity does one B cell have and why?

Answer 15

One specificity

It only has one VDJ and VJ rearrangement and can only bind to one epitope

Question 16

What chromosome do B cell heavy chains recombine on?

Answer 16

14

Question 17

What chromosome do B cell light chains recombine on?

Answer 17

2

Question 18

What are the 2 constant regions for light chains?

Answer 18

Kappa and Lamdba

Only a V and J region

Question 19

How does the immature T cell go from the bone marrow to the thymus, where it can receive its mature receptors?

Answer 19

The adhesion molecules on the surface of immature T cells recognize chemokines and ligands that guide them from the bone to the thymus
They enter the thymus at the cortical region
Once there they will start expressing a T cell receptor, and will then migrate to the medulla where they will learn to recognize antigens that are self

Question 20

What does it mean when a thymocyte is a double negative?

Answer 20

It has first reached the cortex and does not express CD4 or CD8
(quadruple negative says habal)

Question 21

How does immature T cell get its starting location in the thymus to the cortex?

Answer 21

Through CCR 9 (Chemokine receptor 9) on the thymocyte recognizing CCL 25 (Chemokine ligand 25), which is located in the thymic cortex

Question 22

How does the immature T cell stay in the cortex?

Answer 22

VLA 4,5, & 6 will interact with the adhesion molecules to trap the T cell there

Question 23

What does VLA 6 bind with?

Answer 23

Laminins

Question 24

What does VLA 4 and 5 bind with?

Answer 24

Fibronectin

Question 25

When does the thymocyte start acquiring TCR?

Answer 25

In the cortex

Question 26

How does the thymocyte leave the cortex and get to the medulla?

Answer 26

CCL 21 & CCL19 will be recognized by the thymocytes CCR7, pulling the thymocyte into the medulla