T Cells: Receptors, MHC, and Antigen recognition

Question 1

what are the two major classes of T cells

Answer 1

cytotoxic CD8 T cells

helper CD4 T cells

Question 2

The T cell receptor

Answer 2

primarily bind polypeptides
never secreted
incidence detector
no effector function
interacts with MHC complex 
antigens not recognized in isolation(must bind MHC for signal)

Question 3

what are the two classes of T cell receptors

Answer 3

alpha: beta
gamma: delta

Question 4

alpha:beta T cells

Answer 4

classic T cell
adaptive immunity
common in circulation not tissues
develops and matures in thymus
positive and negative selection

Question 5

gamma:delta T cells

Answer 5

not involve in adaptive immunity
monitor tissue health
common in tissues not circulation
develops, but does NOT mature in thymus
limited positive and negative selection 
-one class

Question 6

alpha chain of T cell receptor

similar to light chain of Abs

Answer 6

V, J, C segments

-junctional diversity

Question 7

beta chain of T cell receptor

similar to heavy chain of Abs

Answer 7

V, J, D, C

-junctional diversity

Question 8

how many hypervariable/complementarity-Determining per chain?

Answer 8

3

Question 9

TCR genes are rearranged by what enzymes?

Answer 9

RAG 1/2 complexes

deficient in RAG leads to no T cells

Question 10

what has more total diversity between immunoglobulins and alpha:beta receptors?

Answer 10

alpha:beta T-cell receptors

why? T cell receptor genome is longer

Question 11

What do TCRs require for signal transduction?

Answer 11

CD3

Question 12

CD3 complex

Answer 12

mediates TCR signaling

-NO TCR expression without CD3 complex

Question 13

What does the MHC do?

Answer 13

presents broken down antigens(peptides) to TCRs

Question 14

MHC class I

Answer 14

found on nearly all cells
**presents intracelluar antigen**
alpha and beta2 microglobulin
**-ER antigen loading**
**CD8 co-receptor

Question 15

MHC class II

Answer 15

internalized (phagocytosis)

• on antigen presenting cells ( macs, dendritics, and B cells)
• *vesicular ER loading**
• *CD4 Co-receptor

Question 16

what is another name for MHC

Answer 16

human leukocyte antigen (HLA)

Question 17

will TCRs bind both MHC class I and II?

Answer 17

yes, it is the co-receptor on the T cell that determines MHC class binding

Question 18

what cell does not have any MHC complexes on its surface?

Answer 18

erythrocytes and neurons

Question 19

where does loading occur for MHC class I?

Answer 19

in the ER

Question 20

where does loading occur for MHC class II

Answer 20

VESICULAR ER loading

Question 21

cells that express MHC class II can express MHC class I T/F?

Answer 21

true

Question 22

MHC I: antigen loading in the ER

Answer 22

• heavy chain is stabilized by calnexin until beta 2 binds.
• heavy chain forms peptide loading complex with calreticulin, tapsin, TAP and ERp57
• TAP delivers intracellular peptide to Class I heavy chain forming mature MHC I molecule
• MHC class I dissociates from peptide loading complex and is exported from ER

Question 23

The intracelluar antigen peptides are how many residues?

Answer 23

8-10

• trimmed before expression
• allows detection of intracellular infection

Question 24

MHC I: cross presentation of endocytosed antigen

Answer 24

phagocytic cells that have endocytosed antigen will express both MHC I and II with the same antigen

Question 25

why is cross presentastion important?

Answer 25

important for naive CD8 T cell activation

-also doesn’t allow for intracelluar pathogens to live inside phagocytic cells

Question 26

MHC II: CLIP prevents self antigen presentation how?

Answer 26

• invariant chain blocks binding of peptides to MHC II in the ER
• once inside a vesicle the invariant chain is cleaved, leaving CLIP fragment bound
• CLIP blocks binding of MHC II in vesicle
• HLA-DM facilitates release of CLIP, allowing peptides to bind

Question 27

what blocks bind of MHC II in the ER?

Answer 27

invariant chain

Question 28

what blocks the binding of MHC II in the vesicle?

Answer 28

CLIP

Question 29

what releases the binding of CLIP inside the vesicle?

Answer 29

HLA-DM

Question 30

the T cell synapse

what dictates MCH specificity of T cells

Answer 30

the Co-receptors on the T cells

NOT the TCR

Question 31

what MHC does a CD8 bind?

Answer 31

MHC I on any cell with intracelluar pathogen

Question 32

what MHC does a CD4 bind?

Answer 32

MHC II on a APC

Question 33

T cells have a direct and indirect effector function how?

Answer 33

(direct) CD8s bind intracelluar pathogen infected cell to die
(indirect) -CD4s bind to APCs to release cytokines
(indirect) -CD4s bind to B cells to differentiate into plasma cells to make antibodies