Antigen Recognition by T cells and MHC

Question 1

What is SCID?

Answer 1

Severe combined immunodeficiency syndrome- absence of, or few, functional T cells (humoral immunity also lost)

Question 2

What is Omenn Syndrome?

Answer 2

MIssense mutations in RAG-1 and RAG-2 resulting in partial activity- causes SCID

Question 3

What must happen before the TCR can leave the endoplasmic reticulum?

Answer 3

Association with 4 proteins– the CD3 complex- and the zeta chain

Question 4

What portion of the TCR mediates intracellular signaling?

Answer 4

Associated zeta chain

Question 5

What is the #1 marker for T cells?

Answer 5

CD3

Question 6

What are the 2 mutually exclusive classes of alpha-beta T cells?

Answer 6

CD4+ and CD8+

Question 7

What types of T cells are cytotoxic and kills infected cells?

Answer 7

CD8+

Question 8

What type of MHC presents intracellular pathogens? To what kind of T cells?

Answer 8

Class I; CD8+

Question 9

What type of MHC presents extracellular pathogens? To what kind to T cells?

Answer 9

Class II; CD4+

Question 10

What cells express MHC I ? MHC II?

Answer 10

Almost all cells express Class I; Class II only on macrophages, dendritic cells, and B cells

Question 11

What is antigen processing and presentation?

Answer 11

Antigen processing is the proess by which antigens are cleaved into short peptides that the T cells can recognize; Antigen presentation is the binding of Ag to MHC and movement to the surface

Question 12

What is the structure of the MHC class I? What subunits form the peptide binding site?

Answer 12

Transmembrane alpha chain complexed with beta2 microglobulin; Alpha 1 and alpha 2 form the binding site

Question 13

What is the structure of the MHC class II? What subunits form the peptide binding site?

Answer 13

2 transmembrane proteins- alpha chain and beta chain- both of which contribute to the binding site

Question 14

What is meant by MHC having a ‘promiscuous’ binding specificity?

Answer 14

Their peptide binding sites can bind peptides of many different

Question 15

Which MHC class can bind to larger peptide

Answer 15

Class II

Question 16

How is antigen processed and presented via MHC Class I?

Answer 16

Interferons prompt the proteosome to become an immunoproteosome and degrade intracellular pathogenic protein. The TAP transporter proteins take the peptide into the ER where the peptide is assemble in the groove of MHC I after which is is transported to the surface via the Golgi

Question 17

How is antigen processed and presented through MHC II?

Answer 17

Extracellular material is taken up by phagocytosis into a phagosome which fuses with a lysosome. The phagolysosome degrades the peptide. MHC II enters into the vesicles and are loaded with peptide and transported to the surface

Question 18

True or False: If no pathogenic peptide is available the MHC is loaded onto the surface empty

Answer 18

False: antigen must be loaded to get to the surface

Question 19

What is a superantigen? What kind of molecule are most?

Answer 19

An intact protein that is recognized by the T cells without being processed into peptide; Most are bacterial toxins

Question 20

Why are superantigens so dangerous?

Answer 20

It can activate a large number of CD4+ cells to generate a cytokine storm

Question 21

To what part of the TCR does a superantigen bind?

Answer 21

They bind to specific V beta families

Question 22

What are MHC molecules in humans often called?

Answer 22

HLA- Human Leukocyte Antigen complex

Question 23

How is MHC diversity achieved?

Answer 23

1) Gene families- each individual expresses several genes encoding both classes of MHC 2) Genetic polymorphisms within the genes

Question 24

What are the protein products of different genes in an MHC class I or II family called?

Answer 24

Isotypes

Question 25

What are the major MHC class I isotypes?

Answer 25

HLA-A, HLA-B, and HLA-C

Question 26

What are the major MHC Class II isotypes?

Answer 26

HLA- DP, DQ, and DR

Question 27

What is a haplotype?

Answer 27

The combination of MHC alleles that is inherited from each parent

Question 28

In any mating, how many possible combinations of haplotypes are there?

Answer 28

4

Question 29

Where is most of the polymorphic diversity between MHC allotypes?

Answer 29

Concentration in the sites on the MHC that bind peptide and TCR

Question 30

What are anchor residues?

Answer 30

Amino acids that are conserved throughout all peptides that bind to a particular MHC

Question 31

What is MHC restriction?

Answer 31

The principle of T cell biology that dictates that antigen specific T cell responses are restricted by MHC type

Question 32

True or False: A T cell that responds to a peptide presented by one MHC allotype will not respond to another peptide bound by the same MHC allotype or to the same peptide bound to another MHC allotype

Answer 32

True

Question 33

True or False: Though the fetus is generally protected from maternal immune reponses, mom still makes alloantibodies to paternal MHC.

Answer 33

True

Question 34

What is the dominant geentic factor affecting suscetibility to autoimmune disease?

Answer 34

HLA