7 Anitgen recognition by T cells

Question 1

what are T cells

Answer 1

WBC

Question 2

what do T cells do

Answer 2

play a central role in cell-mediated immunity

Question 3

how are lymphocytes distinguished

Answer 3

can be distinguished from other lymphocytes (B cells), by the presence of a T-cell receptor (TCR) on the cell surface

Question 4

what does a T cell receptor look like

Answer 4

very similar to antibody molecule

T cell receptor structure almost identical to one arm of antibody, and always transmembrane

Question 5

what do T cells recognise

Answer 5

recognise epitopes presented by Antigen Presenting Cells (APC) bearing an MHC molecule, but cannot recognise the peptide alone

Question 6

what do T cell require

Answer 6

requires breakdown of antigens

Question 7

what do immunoglobulins

Answer 7

recognises epitopes on molecules in the blood or lymph or on surface of a pathogen

Question 8

what is TCR for

Answer 8

ONLY for antigen recognition - then sends signal to T-cell

Question 9

what type of molecule is immunoglobulin

Answer 9

effector molecule

Question 10

what is MHC

Answer 10

antigen recognition molecule

Question 11

what does MHC encode

Answer 11

Large number of genes which encode class I and class II molecules (called antigen presenting molecules) + associated molecules

Question 12

what are MHC evolved for

Answer 12

for antigen presentation to T-cells

Question 13

what does MHC class 1 present to

Answer 13

CD8+ cytotoxic cells

Question 14

what does MHC class 2 present to

Answer 14

CD4+ helper cells

Question 15

what are cytotoxic cells function

Answer 15

kill virally infected cells

- MHC is on every cell of our body (as every cell could be infected by a virus)

Question 16

MHC class 1 structure

Answer 16

Only 1 alpha chain, with transmembrane region (3 domains)
Peptide binding cleft is part of that alpha chain
Beta 2 microglobulin is a separate molecule which stabilizes structure

Question 17

MHC class 2 structure

Answer 17

Difference is that there are 2 molecules that form cleft

- Beta peptide and an alpha peptide

Question 18

how do T cells recognise peptides

Answer 18

T-Cell receptor binds to peptides when they are presented on the surface of the Antigen Presenting Cell – monospecific

Question 19

what molecules are monospecific

Answer 19

T cells

Question 20

what molecules are polyspecific

Answer 20

MHC

Question 21

what is polyspecific

Answer 21

able to have many peptides bind, can present many peptides in there

Question 22

what are the classes of MHC class 1

Answer 22

3 class I α (A,B and C)

Question 23

what are the pairs of MHC class 2

Answer 23

3 pairs of Class II α and β (DR, DP, and DQ) but can end up with 4 class II groups (in DR can have alpha was beta I or alpha with beta II)

Question 24

what is polygenic

Answer 24

there are several different genes for class I and II

Question 25

what is polymorphic

Answer 25

many alleles for each gene-one of the most polymorphic genes known MANY peptides can be presented to T-cell

Question 26

how many of each MHC class does an individual present

Answer 26

Each individual will present 3 sets of class I molecules and 4 class II

Question 27

which MHC are polymorphic

Answer 27

All MHC products polymorphic except DR-α-reason unknown

Question 28

what will a typical human express - MHC

Answer 28

6 different Class I molecules 8 different Class II For class II α and β chains can combine from different chromosomes

Question 29

what is gene conversion

Answer 29

misalignment in meiosis means copied from a different allele

Question 30

what is gene recombination

Answer 30

Exchange of DNA segments from different chromosomes

Question 31

what is the effects of polymorphism

Answer 31

Variability of peptide expression-allows many thousands of sequences to be presented Rare that a protein has no peptide that can be bound by MHC BOTH peptide MHC complex is recognised by TCR

Question 32

where is the variation between MHC allotypes concentrated

Answer 32

- peptide binding groove where they affect peptide recognition - alpha helices forming walls where affect TCR recognition

Question 33

peptide specificity

Answer 33

Alleles of MHC confer some specificity on the peptide bound

Question 34

where is peptide specificity

Answer 34

2-3 residues that form the ANCHOR sequence

Question 35

length of class 1

Answer 35

only 8-10aa long

Question 36

length of class 2

Answer 36

variable length

Question 37

Class I and II present Ag to different cell types

Answer 37

This is achieved by molecular interactions between the CD4 and CD8 glycoproteins and their respective MHC molecules

Question 38

what are MHC class 1 and 2 known as

Answer 38

coreceptors

Question 39

what do CD4 and CD8 do

Answer 39

- Stabilise/strengthen TCR/MHC interaction | - Transduce signal to T cell

Question 40

affinity of TCR

Answer 40

Affinity of TCR is weak-needs other interactions to strengthen binding

Question 41

cytokine effect on MHC expression

Answer 41

Cytokines increase the expression of MHC molecules-particularly IFN gamma

Question 42

MHC class 1 expression meaning

Answer 42

Class 1 indicates cell is infected by a pathogen so any nucleated cell can express it, make lots of MHC = to be killed

Question 43

MHC class 2 expression meaning

Answer 43

Class II presents peptides to T helper cells so tends to be expressed by professional APCs-macrophages, dendritic cells and B cells

Question 44

How do Peptides get into MHC class 1 molecules

Answer 44

Class I binds molecules come from intracellular viruses and bacteria

Question 45

How do Peptides get into MHC class 2 molecules

Answer 45

Class II can come from intracellular pathogens OR from an extra-cellular source

Question 46

what do MHC have to have when no infection

Answer 46

MHC molecules-HAVE to have a peptide bound in absence of infection-may be self

Question 47

what is the cell divided into 2 compartments

Answer 47

1 Nucleus and cytosol – intracellular | 2 Vesicular system (secretory part) -ER, golgi, endocytic vesicles

Question 48

what is the cell in contact with

Answer 48

extracellular fluid

Question 49

what expresses peptides

Answer 49

- Class I are endogenous-intracellular | - Class II exogenous-extracellular

Question 50

where are class 1 degraded

Answer 50

cytocol

Question 51

where are class 2 degraded

Answer 51

endocytic vesicles

Question 52

mononuclear phagocytes and antigen presentation

Answer 52

phagocytosis, present fragment

Question 53

B cell and antigen presentation

Answer 53

B cells brought through surface Ig

Question 54

dendritic cells and antigen presentation

Answer 54

brought through by pinocytosis

Question 55

Class II and extracellular molecule movement

Answer 55

Class II translocated to ER on way to surface

Question 56

what is done to prevent premature binding of peptides and effect

Answer 56

To prevent premature binding of other peptides the invariant chain binds (also on MHC) also helps MHC get to the low pH endosome where proteins are degraded MHC and endosome fuse, invariant chain cleaved and replaced by peptide

Question 57

why is HLA DM important

Answer 57

needed for T cell activation

Question 58

what is required for MHC class 1

Answer 58

Intracellular peptides require processing

Question 59

where are the antigen processing genes for class 1

Answer 59

in the MHC

Question 60

what is located in the MHC locus

Answer 60

LMP | TAP

Question 61

what forms a proteosome

Answer 61

two LMP units

Question 62

what does the proteosome do

Answer 62

continuously degrades proteins to peptides-from the cytosol including those from pathogens

Question 63

what is proteosome expression induced by

Answer 63

IFN

Question 64

what do TAP 1 and 2 form

Answer 64

complex that selects the peptides that can be transported into the ER

Question 65

where are peptides made

Answer 65

cytosol

Question 66

where are peptides transported

Answer 66

ER