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Immuno > Immuno Exam 2 Chapter 6 > Flashcards

Immuno Exam 2 Chapter 6 Flashcards

1
Q

What cells play an important role in adaptive immune system function?

A

T cells

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2
Q

What cells activate other immune system cells?

A

effector T cells

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3
Q

What other immune system cells are activated by effector T cells?

A

macrophages
neutrophils
B cells

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4
Q

What relies on the action of T cells?

A

pathogen clearance that requires an adaptive immune response

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5
Q

What does MHC stand for?

A

major histocompatibility complex

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6
Q

What presents a specific antigenic peptide?

A

a cell using a MHC protein

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7
Q

What on each T cell interacts with a specific antigenic peptide?

A

surface receptor
coreceptor

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8
Q

What is MHC diversity due to the presence of?

A

MHC gene families and genetic polymorphism
NOT recombination events

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9
Q

What do a wide variety of MHC molecules bind and present?

A

the many antigens that must be displayed to T cells as part of the adaptive immune response

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10
Q

What is the major function of the T-cell receptor?

A

recognize a specific MHC-peptide complex

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11
Q

What does T-cell recognition occur, in part, through?

A

a coreceptor located on the cell surface (CD4 or CD8)

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12
Q

How many types of genes are activated by T-cell receptor:MHC-peptide complex signaling pathways?

A

two

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13
Q

What are the genes activated by T-cell receptor:MHC-peptide complex signaling pathways?

A

those required for proper division and differentiation of the T cell
those required to carry out the effector functions of the activated T cell

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14
Q

What do activated CD8 T cells become, and what do they do?

A

cytotoxic T cells
target cells infected with intracellular pathogens

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15
Q

What do activated CD4 T cells become, and what do they do?

A

helper T cells (TH)
activate cells that combat extracellular pathogens

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16
Q

What are coreceptors CD4 and CD8 important in the recognition of?

A

MHC-peptide complex on an antigen-presenting cell

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16
Q

What are coreceptors CD4 and CD8 important in the recognition of in a location separate from the peptide-binding groove?

A

the MHC-peptide complex on an antigen-presenting cell

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17
Q

What do T-cell receptor proteins lack?

A

a significant cytoplasmic domain

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18
Q

What can T-cell receptors not do?

A

initiate intracellular signaling events on their own

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19
Q

What must T-cell receptors interact with to initiate signaling?

A

other cell-surface molecules (CD4 or CD8 coreceptor, along with the CD3 complex)

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20
Q

What is the CD3 complex composed of?

A

δ, ε and γ chains
two ζ chains

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21
Q

What do the polypeptides composing the CD3 complex recruit?

A

signaling molecules that are activating upon TCR engagement

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22
Q

What is an essential costimulatory signal for naive T-cell activation?

A

CD28

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23
Q

What binds to the same molecule as CD28, down-regulates T-cell activation, and prevents unchecked T-cell activation and effector functions?

A

CTLA4

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24
Q

What can exonucleases do?

A

trim the P nucleotides left in the overhang region of the opened end of the gene segment

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25
Q

What can terminal deoxynucleotidyl transferases (TdT) do?

A

add N nucleotides to the ends of each gene segment (every rearrangement)

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26
Q

What is random?

A

removal of P nucleotides
addition of N nucleotides

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27
Q

What are productive rearrangements?

A

the production of a functional receptor subunit

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28
Q

What are unproductive rearrangements?

A

result in a nonfunctional T-cell receptor subunit

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29
Q

What do checkpoints test for?

A

whether a productive rearrangement has occurred at the α and β loci

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30
Q

What do checkpoint mechanisms promote?

A

further recombination

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31
Q

What will exhaustive unproductive rearrangements lead to?

A

apoptosis

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32
Q

What can be produced during rearrangement?

A

a functional but self-reactive TCR

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33
Q

What may T cells with a self-recognizing receptor that escape the thymus lead to?

A

autoimmune disorders
destruction of healthy tissue

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34
Q

How many subunits are in MHC class I molecules?

A

two

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35
Q

What are the subunits in an MHC class I molecule?

A

α chain
soluble protein β2-microglobulin

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36
Q

What does an α chain of an MHC class I molecule do?

A

anchors the MHC to the plasma membrane

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37
Q

What contains a transmembrane segment?

A

α chain

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38
Q

What does not contain a transmembrane segment?

A

β2-microglobulin

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39
Q

What are the three domains of the α subunit of an MHC class I molecule?

A

α1
α2
α3

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40
Q

The peptide-binding groove of an MHC class I molecule binds peptides ______ amino acids long.

A

8 to 10

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41
Q

How many subunits are in MHC class II molecules?

A

two

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42
Q

What are the subunits in an MHC class II molecule?

A

α and β

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43
Q

What type of peptides are MHC class II subunits?

A

transmembrane polypeptides

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44
Q

What does each of the subunits of an MHC class II molecule fold to form?

A

a peptide-binding groove

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45
Q

What length peptide can the peptide-binding groove of an MHC class II molecule bind?

A

13 to 25 amino acids

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46
Q

What do other portions of each subunit of an MHC class II molecule fold to contain?

A

immunoglobulin-like domains that support the structure of the peptide-binding groove

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47
Q

What does the peptide-binding groove of a T-cell receptor:MHC-peptide complex allow the peptide to do?

A

protrude between the two α-helices

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48
Q

What does the TCR and MHC-peptide complex interaction involve?

A

the bound peptide
a larger surface area composed of the MHC molecule and the bound peptide
the variable regions of both TCR subunits

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49
Q

What are extracellular pathogens cleared by?

A

activation of phagocytes
B cells
antibody production

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50
Q

What recognizes the structural domains on both subunits of MHC class II when peptide is presented?

A

CD4 coreceptor

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51
Q

When are intracellular pathogens cleared?

A

CD8 recognizes the structural domain of the α-subunit of MHC class I on an infected cell

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52
Q

What has CD8 been shown to interact with?

A

β-microglobulin

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53
Q

What is required for clonal selection?

A

T-cell receptor/MHC-peptide/coreceptor complex
co-stimulation

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54
Q

What T-cell receptor signaling molecules are required to link the receptor-peptide interaction to signaling events that lead to activation of that cell?

A

CD3 complex
CD28
CD45

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55
Q

What do T-cell signaling molecules do?

A

activate gene transcription that produces cytokines required for activation and differentiation

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56
Q

What is vital to the successful activation of T cells?

A

peptide loading onto MHC molecules

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57
Q

Where are MHC class I molecules loaded with peptides from intracellular proteins?

A

in the endoplasmic reticulum (ER)

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58
Q

After MHC class I molecules are loaded, where do they move to present peptide to CD8 T cells?

A

plasma membrane

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59
Q

What molecules cannot bind to peptides in the ER?

A

MHC II molecules

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60
Q

Where do MHC II molecules move to, and what does it fuse with?

A

a vesicle
phagolysosome

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61
Q

Where are MHC II molecules loaded with peptides from extracellular proteins?

A

phagolysosome

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62
Q

Where do MHC class II molecules move to after they are loaded and present extracellular peptides to CD4 T cells?

A

plasma membrane

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63
Q

Nearly all ______ cells of the body express MHC class I.

A

nucleated

64
Q

How many steps does intracellular peptide loading in the ER take?

A

five

65
Q

What is step one of intracellular peptide loading?

A

formation of the peptide-loading complex

66
Q

Upon entry, what does the α chain bind to during step one of intracellular peptide loading?

A

ER chaperone calnexin

67
Q

Once properly folded, what does the α chain and β2-microglobulin associate with during step one of intracellular peptide loading?

A

peptide-loading complex

68
Q

What is a major player in step one of intracellular peptide loading?

A

tapasin

69
Q

What does the major player of step one of intracellular peptide loading do?

A

allows efficient peptide loading on MHC class I molecules
promotes the association of a peptide that can bind tightly with MHC class I molecules

70
Q

What is another important player in step one of intracellular peptide loading?

A

ER chaperone calreticulin

71
Q

What does the second important player in step one of intracellular peptide loading do?

A

promote proper assembly of MHC class I molecules with the tightly bound peptide

72
Q

What is step two of intracellular peptide loading?

A

digestion of proteins by the proteasome

73
Q

What does the proteasome do?

A

cleaves intracellular proteins into small peptides of varying lengths

74
Q

What produces the immunoproteasome?

A

cytokines secreted during an inflammatory response

75
Q

What do the subunits of the immunoproteasome do during step two of intracellular peptide loading?

A

promote MHC class I presentation at the surface of cells

76
Q

What immunoproteasome subunit aids in processing MHC class I molecules during step two of intracellular peptide loading?

A

11S

77
Q

What immunoproteasome subunits generate peptides 8 to 10 amino acids long during step two of intracellular peptide loading?

A

β

78
Q

What is step three of intracellular peptide loading?

A

peptide transport into the ER

79
Q

Where are peptides generated by the proteasome or immunoproteasome first released into in step three of intracellular peptide loading?

A

cytosol

80
Q

Why must peptides be transported into the ER during step three of intracellular peptide loading?

A

to be loaded on MHC class I molecules

81
Q

What is a transporter associated with antigen processing (TAP)?

A

peptide transporter in the ER membrane

82
Q

What does a TAP do during step three of intracellular peptide loading?

A

carries proteasome-derived peptides into the ER where they can interact with MHC class one molecules

83
Q

What is step four of intracellular peptide loading?

A

peptide trimming

84
Q

What does tapasin do in step four of intracellular peptide loading?

A

functions in the peptide-loading complex to ensure that a tightly bound peptide is engaged in the peptide-binding groove of an MHC class I molecule

85
Q

What happens to some peptides that are produced too long to fit the peptide-binding groove during step four of intracellular peptide loading?

A

ERAP, another protease in the ER, trims the N-terminal end of the overhanging peptide to the length needed

86
Q

What does ERAP stand for?

A

endoplasmic reticulum aminopeptidase

87
Q

How many amino acids are needed for tight binding to the peptide-binding groove?

A

8 to 10

88
Q

What is step five of intracellular peptide loading?

A

transport to the plasma membrane

89
Q

How is an MHC class I molecule loaded with peptide transported during step five of intracellular peptide loading?

A

via vesicles through the secretory pathway through the Golgi apparatus before its cargo vesicle fuses with the plasma membrane

90
Q

Where is the loaded MHC class I molecule expressed on?

A

plasma membrane

91
Q

What does the loaded MHC class I molecule wait for during step five of intracellular peptide loading?

A

a CD8 T cell bearing a TCR that can recognize the MHC-peptide complex

92
Q

What do MHC class II molecules present?

A

peptides from extracellular proteins on the surface of APCs
macrophages, dendritic cells, and B cells

93
Q

Where do MHC class II molecules begin in?

A

the secretory pathway

94
Q

When are MHC class II molecules loaded?

A

not until they are part of the vesicle capable of fusing with a phagosome

95
Q

How many steps does MHC class II peptide loading take?

A

four

96
Q

What is step one of MHC class II peptide loading?

A

MHC class II molecule assembly in the ER

97
Q

Despite being in the ER, what are class II molecules not loaded with?

A

intracellular peptides

98
Q

What is an invariant chain in regards to step one of MHC class II peptide loading?

A

a protein that assembles with MHC class II in the ER and blocks the peptide-binding groove
prevents binging binding of proteasomal peptides

99
Q

What is step two of MHC class II peptide loading?

A

clip production

100
Q

Where are MHC class II molecules transported during step two of MHC class II peptide loading?

A

the MHC compartment

101
Q

What cleaves the invariant chain during step two of MHC class II peptide loading?

A

protease cathepsin S

102
Q

What does the protease that cleaves the invariant chain leave bound to the peptide-binding groove?

A

a peptide called the class II-associated invariant chain peptide (CLIP)

103
Q

Where does the endosome CLIP remain until fusion with a phagolysosome?

A

in an intracellular pool

104
Q

What is step three of MHC class II peptide loading?

A

phagocytosis and fusion with the MHC compartment

105
Q

What happens during step three of MHC class II peptide loading?

A

phagocytes engulf pathogens and internalize them in phagosomes

106
Q

What does each phagosome in step three of MHC class II peptide loading do?

A

fuses with a lysosome, acidifies, and becomes a phagolysosome

107
Q

What does protease activity within the phagolysosome generate?

A

peptides from ingested material (extracellular material)

108
Q

What does the phagolysosome fuse with during step three of MHC class II peptide loading?

A

MHC compartment

109
Q

What is step four of MHC class II peptide loading?

A

peptide loading

110
Q

What are MHC class II molecules in the fused vesicle still bound do in step four of MHC class II peptide loading?

A

CLIP

111
Q

What promotes the exchange of CLIP for lysosomal peptides during step four of MHC class II peptide loading?

A

HLA-DM (human leukocyte antigen DM)

112
Q

Where do the vesicle and MHC class II molecule and peptide travel to during step four of MHC class II peptide loading?

A

plasma membrane

113
Q

What does the loaded MHC class II molecule wait for in step four of MHC class II peptide loading?

A

a CD4 T cell bearing a TCR capable of recognizing the MHC-peptide complex

114
Q

What cells express the costimulatory receptor and can stimulate naive CD4 and CD8 T cells at any time?

A

dendritic cells

115
Q

Most cells only express which molecule during an inflammatory response?

A

costimulatory

116
Q

What drive expression of costimulatory molecules on a potential APC?

A

cytokines

117
Q

If an intracellular pathogen is phagocytosed, how are the peptides from the intracellular pathogen presented by MHC class I molecules?

A

phagocytic cells can use cross-presentation to present phagocytosed material via MHC class I molecules

118
Q

Where is phagocytosed material typically presented via?

A

MHC class II molecules

119
Q

What are examples of phagocytic cells?

A

especially dendritic cells
macrophages
B cells

120
Q

What does cross-presentation activate?

A

CD8 T cells responsible for combating the intracellular infection

121
Q

What is cytosolic diversion?

A

endocytosed material in a cross-presenting cell is transported to a specialized endosome and ends up in the cytosol

122
Q

How can diverted material in the cytosol be processed and presented?

A

using the normal MHC class I machinery

123
Q

What is cross-presentation believed to play an important role in?

A

activating naive CD8 T cells required to mount an adaptive immune response to an intracellular pathogen such as virus

124
Q

Why must a dendritic cell be licensed?

A

to properly cross-present antigen

125
Q

What is licensing of cross-presentation in dendritic cells postulated to require?

A

CD4 T cells

126
Q

What is the mechanism required for the licensing of cross-presentation in dendritic cells?

A

dendritic cells present phagocytosed extracellular antigens on MHC class II and activate a naive CD4 T cell
activated CD4 T cells release cytokines, signaling the dendritic cell to begin cross-presentation, potentially activating naive CD8 T cells

127
Q

What is mice H-2 (histocompatibility 2) analogous with in humans?

A

HLA (human leukocyte antigen)

128
Q

What parallel the diversity seen in TCRs?

A

MHC molecules

129
Q

What is MHC diversity driven by?

A

genes and the presence of different alleles for each gene and their expression

130
Q

The proteins expressed by the gene familiar for each MHC class are known as ______.

A

isotypes

131
Q

How are MHC alleles expressed?

A

codominantly

132
Q

The proteins expressed by MHC alleles are ______.

A

allotypes

133
Q

What do all the alleles of every MHC class I and class II gene make up?

A

a person’s haplotype

134
Q

What provides a person’s overall MHC diversity?

A

haplotype

135
Q

How many MHC class I isotypes are there in humans?

A

six

136
Q

What are the MHC class I isotypes in humans?

A

HLA-A
HLA-B
HLA-C
HLA-E
HLA-F
HLA-G

137
Q

What do all human MHC class I isotypes have?

A

immune function, but a different focus

138
Q

If considering the alleles of the first three human MHC class I isotypes, how many different haplotypes are there for MHC class I?

A

5.1x10^11

139
Q

How many MHC class II isotypes are there in humans?

A

five

140
Q

What are the MHC class II isotypes in humans?

A

HLA-DM
HLA-DO
HLA-DP
HLA-DQ
HLA-DR

141
Q

What play different roles within the immune system?

A

class II isotypes

142
Q

If considering the alleles of MHC class II, how many haplotypes are there?

A

1.6x10^23

143
Q

What is the total number of possible haplotypes in the human genome (since class I and class II are both present)?

A

8.2x10^34

144
Q

What make the alleles associated with MHC isotypes highly polymorphic?

A

changes within the peptide-binding groove
not due to random muations

145
Q

What does the peptide-binding motif allow for?

A

flexibility regarding most amino acids within the bound peptide

146
Q

What do anchor residues do?

A

support peptide binding to a specific isotype and limit flexibility
key amino acid requirements in a peptide

147
Q

What may infectious disease act as a selective pressure on the maintenance of within an individual and in a population?

A

MHC heterozygosity (variation of alleles)

148
Q

What does a diverse array of heterozygosity limits?

A

the presence of a susceptible MHC allele

149
Q

What does a diverse array of heterozygosity confer?

A

genetic herd immunity

150
Q

What is the advantage of heterozygosity?

A

more peptides from the pathogen can be displayed, providing a higher potential for T cells to be activated during infection

151
Q

Because heterozygosity is advantageous in the body’s defense against any given pathogen, it is selected for through ______.

A

balancing selection

152
Q

What is a drawback of heterozygosity?

A

increased variety of MHC molecules can lead to complications during infectious disease outbreaks and in organ and tissue transplantation

153
Q

What will the new SARS-CoV-2 virus drive selection of?

A

MHC alleles that are most capable of presenting viral peptides
comes at the expense of heterozygosity

154
Q

What is the shift in selective pressure referred to as?

A

directional selection

155
Q

What is a danger of heterozygosity?

A

introduction of allogeneic MHC molecules can elicit an adaptive immune response which results in rejection of transplanted tissues and organs

156
Q

What does allogeneic mean?

A

from the same species but genetically different

157
Q

What can MHC heterozygosity severely complicate?

A

medical conditions that require tissue or organ transplantation

158
Q

What minimizes the risk of tissue rejection and slows rejection but still requires immunosuppressive drugs?

A

allotype matching

Immuno (2 decks)

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