chapter 7 Flashcards

1
Q

Glycoproteins expressed on all nucleated cells: interact with Tc (CD8+ T ) cells

A

Class I MHC genes

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2
Q

Glycoproteins expressed APC cells: interact with TH (CD4+ T) cells.

A

Class II MHC genes

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3
Q

Secreted protein: complement and tumor necrosis factor (TNF)

A

Class III MHC genes

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4
Q

-Member of the Ig superfamily
-Larger 45 kDa glycoprotein α chain
-Smaller 12 kDa β2-microglobulin protein
-peptide binding groove between α1 and α2 domains

A

Class I molecules

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5
Q

-Member of the Ig superfamily
-Heterodimeric: 33 kDa α chain & 28 kDa β chain
-Both chains pass through the plasma membrane
-A peptide-binding cleft is formed by the pairing of the
α1 and β1 domains

A

class 2 molecules

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6
Q

occurs when two or more clearly different phenotypes
exist in the same population of a species

A

Polymorphism

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7
Q

Where do class I and class II molecules exhibit polymorphism?

A

in the peptide-binding region

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8
Q

How many class I and class II molecules can be expressed per person?

A

up to 6 class I and 12 class II

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9
Q

How does the limited group of molecules (class I & 2) present the vast diverse array of possible antigen peptide fragments?

A

A given MHC molecule can bind numerous different peptides, and some peptides can bind to several different MHC molecules

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10
Q

Describe the Class I MHC-peptide interactions:

A

-present peptides to CD8+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR

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11
Q

Describe the Class II MHC-peptide interactions:

A

-present antigen peptides to CD4+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR

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12
Q

What is the difference between class I and II regarding the nature of the peptide-binding groove?

A

MHC I is closed at both ends
MHC II is open at both ends

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13
Q

What is the size difference between class I and class II molecules?

A

class I is 8-10 amino acids
class II is 13-18 amino acids

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14
Q

describe the peptide motifs involved in binding to the MHC molecule for class I:

A

-anchor residues at both ends of peptide
-generally hydrophobic carboxyl-terminal anchor

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15
Q

describe the peptide motifs involved in binding to the MHC molecule for class II:

A

conserved residues distributed along the length of the peptide

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16
Q

describe the nature of bound peptide for class I:

A

extended structure in which both ends interact with MHC groove but middle arches up away from MHC molecule

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17
Q

describe the nature of bound peptide for class II:

A

extended structure that is held at a constant elevation above the floor of the MHC groove

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18
Q

describe the gene sequence of class I:

A

-5’ leader exon for signal peptide followed by 5–6 exons
encoding α chain
–Signal peptide is eventually removed

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19
Q

one of a number of alternative forms of the same gene or
same genetic locus (a group of genes)

A

allele

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20
Q

what is a haplotype?

A

each set of allele

21
Q

what is the definition of inbreeding?

A

-reproduction from the mating of parents who are closely
related genetically

22
Q

______________________ of mice has allowed for more standardized MHC genotypes to control variability

A

Inbreeding

23
Q

Why are MHC alleles codominantly expressed?

A

-this gives the best chance for an organism to have some capability of presenting all the possible antigen peptides it encounters

24
Q

Why does codominant expression of MHC alleles make transplantation somewhat dificult?

A

humans are heterozygous at each locus

25
Q

How does diversity of class I/II molecules at individual and species levels provide flexibility?

A

This diversity provides flexibility in responding to
unexpected environmental changes, now and in the
future

26
Q

Describe the antigen peptides presented by MHC class I:

A

-intracellular
-includes self peptides
-provides a way for checking that cells are self and are generally healthy
-Can also be used to show which cells have been infected with
viruses or are abnormal

27
Q

Describe the antigen peptides presented by MHC class II:

A

-extracellular
-more restricted
-generally found on APC

28
Q

MHC class II is primarily restricted to _________________.

A

antigen-presenting cells (APC)

29
Q

How can MHC expression change with genetic regulatory components?

A

promoters that drive up transcription during times of infection

30
Q

How can MHC expression change with viral interference?

A

viruses like to shut down MHC Class I expression

31
Q

How can MHC expression change with cytokine-mediated signaling?

A

some cytokines expressed during infection/disease can drive up/down MHC expression

32
Q

How do class II MHC alleles play a critical role in immune responsiveness?

A

Different capability to present antigens may dictate overall strength of response from individual to individual

33
Q

T cells are restricted to recognizing peptides
presented in the context of ____________________.

A

self MHC alleles

34
Q

the property of recognizing antigenic (foreign)
peptides only in the context of self MHC molecules

A

Self-MHC restriction

35
Q

Only _____________antigen peptide fragments can be recognized by T cells.

A

processed

36
Q

What type of processing is required for Class I presentation?

A

cytosolic or endogenous processing

37
Q

What type of processing is required for Class II presentation?

A

exogenous processing

38
Q

Describe the endogenous pathway of antigen processing and presentation:

A

-peptides are generated by proteasomes then tagged by Ubiquitin for degradation by proteasomes
-peptides are transported from the cytosol to the RER by TAP molecules

39
Q

What are TAP molecules?

A

Transporter associated with antigen processing in the RER membrane that move fragments

40
Q

cleaves ubiquitinated proteins into fragments that pair better with MHC molecules

A

immunoproteasome

41
Q

How do chaperones aid peptide/MHC class I assembly?

A

-Calnexin, calreticulin, and tapasin help fold MHC class I and put it in close proximity to TAP
-ER aminopeptidase ERAP1 trims long peptides to a suitable
size for MHC class I grooves

42
Q

Describe the exogenous pathway of antigen processing and presentation:

A

-peptides are generated from internalized antigens in endocytic vesicles
-particles are taken in with endosomes
-simultaneously, MHC class II molecules are produced and exported from the ER in vesicles

43
Q

How does the invariant chain guide transport of class II MHC molecules to endocytic vesicles?

A

– Invariant chain (Ii, CD74) prevents peptides from
binding to the groove too early in the ER
– Ii also uses sorting signals in its cytoplasmic tail to
direct MHC class II molecule

44
Q

What is the primary cross-presenting cell type?

A

dendritic cells

45
Q

Describe cross-presentation of exogenous antigens:

A

– Exogenous antigens are redirected to the endogenous presentation pathway
– This allows for their presentation on MHC class I molecules,
priming CD8+ T-cell responses
– Dendritic cells are the only APCs (so far) to exhibit this activity
in vivo

46
Q

What is the mechanism and function of cross-presentation?

A

-To prevent redirection of self-antigens into APC pathways, dendritic cells may need “license”
-If DC can present foreign antigen to
CD4+ helper T cell, it gets “license” to redirect exogenous Ag into the endogenous pathway
-“License” might be back/forth cytokine signal between the APC and helper T cell, a situation right for cross-presentation

47
Q

How are nonprotein antigens recognized by T cells?

A

they load on the CD1 family

48
Q

what is the definition of homozygous?

A

having the same alleles at a particular gene locus on homologous chromosomes

49
Q

what is the definition of heterozygous?

A

having different alleles at one or more corresponding
chromosomal loci