Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Immunology Test II > Lymphocyte Development and Ag receptor Gene Rearrangement Part II > Flashcards

Lymphocyte Development and Ag receptor Gene Rearrangement Part II Flashcards

1
Q

Before birth, B lymphocytes develop from committed precursor in what organ?

A

The fetal liver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

After birth, where are B lymphocytes generated?

A

In the bone marrow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Arising from adult bone marrow, what do progenitors initially not have?

A

Do not express Ig

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

When do immature B cells leave the bone marrow to further develop?

A

When immature B cells express membrane-bound IgM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

After leaving the bone marrow, immature B cells primarily go to mature further where?

A

In the spleen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How long does it take for the development of a mature B cell from a lymphoid progenitor?

A

Estimated to take 2 to 3 days

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the earliest bone marrow cell committed to the B cell lineage?

A

Pro-B cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Pro-B cells do not produce ___

A

Ig

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are first expressed on pro-B cell?

A

Rag-1 and Rag-2 proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In pro-B cells, the first recombination of Ig genes occurs at what locus ?

A

At the heavy chain locus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the function of the TdT enzyme?

A

Catalyzes the non-templated addition of junctional N nucleotides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When is the TdT enzyme expressed most abundantly?

A

During the pro-B stage when VDJ recombination occurs at the lg H locus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When do levels of TdT decrease?

A

Before L chain gene V-J recombination is complete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Junctional diversity attributed to the addition of N nucleotides is more prominent in the rearrangement of what genes?

A

More in H chain genes than in light chain genes since TdT is most abundantly expressed during VDJ recombination at the lg H locus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does the H chain C region exons remain separated from the VDJ complex?

A

By DNA containing the distal J segments and the J-C intron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

The rearranged Ig H chain gene is transcribed into what?

A

A primary transcript that includes the rearranged VDJ complex and the C μ exons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does the C μ nuclear RNA undergo?

A

Undergoes splicing in which the introns are removed and exons joined together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

For a rearrangement to be productive (in the correct reading frame) what must happen?

A

Bases must be added or removed at junctions in multiples of three

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How many of all pro-B cells make productive rearrangements at the lg H locus?

A

about 50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What cells survive and differentiate further?

A

Only cells that make productive rearrangements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

When are pre-BCRs expressed?

A

During the pre-B cell stage of maturation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the pre-BCR composed of?

A

μ IgH chains and an invariant surrogate IgL chain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the surrogate IgL chain composed of?

A

The V pre-B protein ( a homolog of a variable domain of IgL)

And λ5 protein (a homolog of a constant domain of IgL)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How is the λ5 protein attached to the μ IgH chain?

A

Covalently attached by a disulfide bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the pre-BCR associated with?

A

The Igα and Igβ signaling molecules that are part of the BCR complex in mature B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What forms the pre-BCR?

A

Complexes of μ IgH, surrogate IgL chains and Igα and Igβ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What do invariant λ5 and V pre-B proteins composed? What are they structurally homologous to?

A

They compose the surrogate IgL chain

Invariant λ5 and V pre-B proteins are structurally homologous to k and λ light chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Igα and Igβ also form part of what in mature B cells?

A

B cell receptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are responsible for the largest proliferation expansion of B lineage cells in the bone marrow?

A

Signals from the pre-BCR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What Ag is recognized by the pre-BCR?

A

It is not known

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

It is speculated that pre-BCR is activated by what?

A

By the process of assembly in a ligand-independent manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How is the importance of pre-BCRs illustrated?

A

Illustrated by markedly reduced numbers of mature B cells in KO mice deficient in μ Igh or surrogate IgL chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Rearrangement of IgH locus is initiated at what stage?

A

pro-B-cell stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

If rearrangement of IgH locus is successful, what will it give rise to?

A

The Ig μ chain that is expressed on the cell surface in the form of the pre-B cell receptor at the large pre-B cell stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What does signaling from the pre-BCR induce?

A

Clonal proliferation and recombination of (IgL) genes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What results in the expression of a complete BCR on immature B cells?

A

In-frame IgL gene rearrangements in small pre-B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is the first checkpoint in B cell maturation?

A

The expression of the pre-BCR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

A number of signaling molecules linked to pre-BCR are required for what?

A

For cells to successfully negotiate the pre-BCR-mediated checkpoint at the pro-B to pre-B cell transition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What kinase is activated downstream of the pre-BCR?

A

Bruton’s tyrosine kinase (Btk)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is Btk required for?

A

For the delivery of signals from this receptor that mediate survival, proliferation, and maturation at and beyond the pre-B cell stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What does mutations in the Btk gene result in?

A

A disease called x-linked agammaglobulinemia (XLA), which is characterized by a failure of B cell maturation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

If a μ IgH is produced from one chromosome and forms a pre-BCR, what does this receptor signal?

A

Signals to irreversibly inhibit rearrangement of the IgH chain locus on the other chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What does allelic exclusion involve?

A

involves changes in chromatin structure in the IgH chain locus that limit accessibility to the V(D)J recombinase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

An individual B cell can express an IgH chain protein encoded by what?

A

ONLY ONE of the two inherited alleles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What happens to the other IgH chain allele not expressed by B cells?

A

It is retained in the germline configuration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What occurs if both alleles undergo nonproductive IgH gene rearrangements?

A

A pre-BCR dependent survival signal is not generated and the cell dies by apoptosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Following the pre-B cell stage, each developing B cell initially rearranges what?

A

a k IgL gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

If the rearranged k IgL gene is productive, what will it produce?

A

Produce a k IgL protein, which associates with the previously synthesized μ IgH to produce a complete IgM protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What does the production of k IgL protein prevent?

A

Prevents λ rearrangement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

How many of the two types (k and λ) of IgL can be expressed?

A

Only ONE, The phenomenon is called light chain isotype exclusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

If the rearrangement of k locus is nonproductive, what happens?

A

The cell can rearrange the λ locus to produce a complete IgM molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What happens if both k and λ chains are nonfunctional?

A

The developing B cell don’t receive survival signals that are normally generated by the BCR and dies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

The assembled IgM (BCR) is associated with what in the BCR complex?

A

Igα and Igβ (signaling subunits)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What does the assembled BCR provided?

A

Ag-independent tonic signals that keep the B cell alive and also mediate the shut off of RAG gene expression that prevents further Ig gene rearrangement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

In response to Ags, what do immature B cells do?

A

They DO NOT proliferate and differentiate
Instead, if BCRs recognize Ags in the bone marrow with high avidity, the B cells may undergo receptor editing or apoptosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Receptor editing or apoptosis are important for what?

A

Negative selection of strongly self-reactive B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

What happens to B cells that are not strongly self-reactive?

A

They leave the bone marrow and complete their maturation in the spleen before migrating to other peripheral lymphoid organs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Immature B cells that recognize self Ags with high avidity may be induced to do what?

A

Change their specificities by a process called receptor editing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

Ag recognition by immature B cells induce reactivation of RAG genes and what?

A

the rearrangement and production of a new Ig light chain, allowing the cell to express a different (edited) B cell receptor that is not self-reactive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

What happens to the original VJk exon encoding the IgVL chain gene that was self reactive?

A

It is typically deleted and replaced by a new rearrangement involving an upstream Vk and a downstream Jk gene segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

If the editing process fails to generate an in-frame productive k IgL, what happens?

A

The activated immature B cell may then go on to rearrange the λ light chain locus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Almost all B cells bearing λ light chains are cells that were once what?

A

Self-reactive and have undergone receptor editing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

If receptor editing fails, what happens?

A

The immature B cells that express high-affinity receptors for self Ags die by apoptosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

What is the process called that follows receptor editing failure?

A

Negative selection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

The Ags mediating negative selection are usually what?

A

Abundant or polyvalent self Ags such as nucleic acids, membrane bound lipids and membrane proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

What are responsible for maintaining B cell tolerance to self Ags that are present in the bone marrow?

A

Receptor editing and negative selection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

What do most B cells that differentiate into B-1 lineage develop from?

A

Fetal liver-derived stem cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

B lymphocytes that give rise to the B-2 lineage arise from what?

A

Bone marrow precursors after birth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

The affinity of the BCRs for self Ags may contribute to differentiation into:

A

Follicular B cells and Marginal zone B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

What are recirculating lymphocytes?

A

Follicular B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

What cells are abundant in the spleen and also are found in LNs?

A

Marginal zone B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

B1 and B2 B cell lineages seem to be ________ regulated and undergo tightly controlled developmental processes

A

Independently

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

What do B1 B cells develop from?

A

HSCs in the bone marrow or fetal liver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

What B cells are self-renewing and produce natural Abs involved in self-defense?

A

B1 B cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

Where do B2 B cells develop from?

A

From HSCs in the bone marrow

76
Q

When do immature B2 B cells relocate to the spleen?

A

Following rearrangement of their BCR chain genes and removal of autoreactive cells via central tolerance

77
Q

Immature B2 B cells that escape the processes of peripheral tolerance differentiate into:

A

MZ B cells or mature follicular B2 cells

78
Q

What B cells develop into long-lived plasma cells or memory B cells upon T-cell-dependent activation?

A

Only mature follicular B2 cells

79
Q

Where are marginal zone (MZ) B cells localized?

A

To the splenic marginal zone

80
Q

What do MZ B cells respond to?

A

Bloodborne Ags

Responses are independent of T cell help

81
Q

What do follicular B cell respond to?

A

Protein Ags in a T cell-dependent manner

82
Q

Which B cells progressively undergo immunoglobulin isotype switching and affinity maturation?

A

Follicular B cells

83
Q

Which B cells comprise a much smaller population?

A

B-1 B cells

84
Q

What B cells predominates in the pleural and peritoneal cavities and contributes most of the serum IgM during the early phases of infection?

A

B1 B cells

85
Q

What B cells are predominantly self-renewing?

A

MZ and B-1 B cells

86
Q

Which B cell needs constant replenishment from bone marrow?

A

Follicular B cells

87
Q

What B cells develop from fetal liver-derived HSCs?

A

B-1 cells

88
Q

What B cells expresses limited BCR diversity and why?

A

B-1 cells because TdT is not expressed in the fetal liver

89
Q

A large number of B-1 cells are found as what?

A

Self-renewing populations in the peritoneum and mucosal sites

90
Q

B-1 cells develop when?

A

Earlier during ontogeny than FBCs and MZ B cells do

91
Q

What do B-1 cells spontaneously secrete?

A

Secrete IgM Abs that often react with microbial polysaccharides and lipids as well as oxidized lipids

92
Q

IgM secreted by B-1 cells are sometimes called what?

A

Natural antibodies because they are present in individuals without overt immunization

93
Q

What do most mature B cells belong to? What do they produce?

A

The FBC subset and produce both IgM and IgD with the same Ag specificity

94
Q

What do FBC coexpress?

A

μ and δ IgH using the same VDJ exons and same k or λ IgL to produce two membrane receptors

95
Q

How is simultaneous expression of IgM and IgD in a single B cell achieved?

A

By alternative RNA splicing

96
Q

A long primary RNA transcript (pre mRNA) containing what?

A

The rearranged VDJ unit as well as both Cμ and Cδ genes

97
Q

What allows a B cell to simultaneously produce mature mRNAs and proteins of two different heavy chain isotopes?

A

Selective polyadenylation and alternative splicing

98
Q

Where are MZ B cells located?

A

Primarily in the vicinity of the marginal sinus of the spleen

99
Q

Similar to B-1 cells, MZ B cells have BCRs of what?

A

limited diversity which respond to polysaccharide Ags and to generate natural Abs

100
Q

What two places can MZ B cells be found?

A

Spleen and lymph nodes

101
Q

What do MZ B cells respond very rapidly to?

A

Blood-borne microbes

102
Q

What do MZ B cells differentiate into after Ag activation?

A

Short-lived IgM-secreting plasma cells

103
Q

Although MZ B cells generally mediate T cell-independent humoral immune responses to circulating pathogens, they also appear capable of what?

A

Mediating some T cell-dependent immune responses

104
Q

The development of mature T lymphocytes from committed progenitors involves:

A

The sequential rearrangement and expression of TCR genes
Cell proliferation
Antigen-induced selection
Commitment to phenotypically and functionally distinct subsets

105
Q

Is T cell maturation similar to B cell maturation.

A

Yes, in many ways

106
Q

What does the thymic environment provide?

A

Provides stimulii that are required for the proliferation and maturation of thymocytes

107
Q

What is the unique feature of T cell maturation?

A

It is the selection of mature T cells with specificity for self MHC-associated peptide Ags

108
Q

What is the major site of maturation of T cells?

A

The thymus

109
Q

The thymus as a major site for T cell maturation was first suspected why?

A

Because of immunologic deficiencies associated with the lack of a thymus (DiGeorge syndrome)

110
Q

If the thymus is removed from a neonatal mouse, what happens?

A

This animal fails to develop mature T cells

111
Q

The thymus involutes with age and is virtually undetectable in post-pubertal humans resulting in what?

A

In a somewhat reduced output of mature T cells, however, maturation of T cells continues throughout adult life

112
Q

Why is there a reduced output of mature T cells post-puberty?

A

Because memory T cells have a long lifespan (perhaps longer than 20 years) and accumulate with age
The need to generate new T cells decreases as individuals age

113
Q

What do T lymphocytes originate from?

A

From precursors that arise in the fetal liver and adult bone marrow and seed the thymus

114
Q

Describe the precursors for T lymphocytes

A

Multipotent progenitors that enter the thymus from the blood stream

115
Q

What are developing T cells in the thymus called?

A

Thymocytes

116
Q

Where does maturation of thymocytes mostly occur?

A

Occurs in the cortex region of the thymus

117
Q

What do αβ T cells mature into?

A

Either CD4 class II MHC-restricted or CD8 Class I MHC-restricted T cells as they leave the cortex, enter the medulla and exit the thymus through the circulation

118
Q

Where do many stimuli required for the proliferation and maturation of thymocytes come from?

A

Other thymic cells

119
Q

What do thymic cortical epithelial cells form?

A

A meshwork of long cytoplasmic processes which allows physical interactions with thymocytes necessary for their maturation

120
Q

What do epithelial cells present in the medulla serve a unique role as?

A

As APCs for the negative selection of developing T cells

121
Q

Where are bone marrow-derived DCs present?

A

At the cortico-medullary junction and within the medulla

122
Q

Where are macrophages present primarily?

A

Within the medulla

123
Q

What do epithelial cells, DCs, and Mo in the thymus express? How are they important?

A 
Class I and class II MHC molecules 
They are important for the selection of the mature T cell repertoire
124
Q

What is the movement of cells into and through the thymus driven by?

A

Chemokines

125
Q

What chemokine recognized on precursors control the entry into the thymus?

A

CCL25,

It is recognized by the CCR9 on precursors

126
Q

What are recognized by thymocytes that mediate the guided movement of developing T cells from the cortex to the medulla?

A

CCL21 and CCL19 are recognized by thymocytes via CCR7

127
Q

What do generated T lymphocytes express to exit the thymic medulla? How does this work?

A

Express sphinosine-1 phosphate receptor and exit the thymic medulla
They follow a gradient of sphingosine-1 phosphate into the blood stream

128
Q

What induces the proliferation of thymocytes?

A

IL-7 produced by epithelial and other stromal cells

129
Q

The rates of cell proliferation and apoptotic death are extremely (high/low) in cortical thymocytes

A

HIGH

130
Q

95% of thymocytes die by apoptosis due to:

A
  1. failure to rearrange the TCR β chain gene
  2. failure to be positively selected by self MHC molecules
  3. self-Ag-induced negative selection
131
Q

Precursors of T cells travel from the _______ through the _____ to the ______

A

Bone marrow
Blood
Thymus

132
Q

In the thymic cortex, progenitors of αβ T cells express what?

A

TCRs and CD4 and CD8 coreceptors

133
Q

What does negative selection eliminate?

A

Twice self-reactive T cells in the cortex at the double-positive (DP) stage and also single-positive (SP) thymocytes in the medulla

134
Q

What do TCRs bind to that promotes survival of thymocytes?

A

TCRs bind to self MHC molecules with low affinity to promote survival

135
Q

Where does functional and phenotypic differentiation into CD4+CD8- or CD8+CD4- T cell occur?

A

Occurs in the medulla, and mature T cells are released into the circulation

136
Q

What do some double-positive cells differentiate into?

A

regulatory T cells

137
Q

What do cortical thymocytes contain?

What are these cells called?

A

TCR genes in their germline configuration and do NOT express TCR, CD3, ζ chains, CD4, or CD8

These cells are called double-negative thymocytes and are considered to be pro-T cells

138
Q

What are first expressed in the double-negative stage of T cell development?

A

Rag-1 and Rag-2

139
Q

What are Rag-1 and Rag-2 required for?

A

The rearrangement of TCR genes

140
Q

What rearrangement of the β chain locus occurs first?

A

The DJ

141
Q

When do V(DJ) rearrangement occur?

A

At the pro-T to pre-T stage transition during αβ T cell development

142
Q

90% of the double-negative thymocytes that survive thymic selection will ultimately give rise to what?

A

To αβ TCR CD4+ and CD8+ T cells

143
Q

What will the other 10% of double-negative thymocytes that survive thymic selection give rise to?

A

γδ T celsl

144
Q

When are pre-T cell receptors expressed?

A

During the pre-T cell stages of maturation

145
Q

What is the pre-T cell receptor composed of?

A

The TCR β chain and the invariant pre-T α (pTα) chain

146
Q

What does the pre-T cell receptor associate with that are part of the TCR complex in mature T cells?

A

With the CD3 and ζ proteins

147
Q

What does the pre-TCR mediate?

A

The development and selection of pre-T cells

148
Q

What do signals from the pre-TCR mediate?

A

The survival of pre-T cells and contribute to the largest proliferation during T cell development
Also β chain allelic exclusion

149
Q

What do pre-TCR signals initiate and drive?

A

TCR α chain locus recombination (a second wave of RAG expression)
Drives the transition for double-negative to the double-positive stage of thymocyte development

150
Q

How is pre-TCR signaling initiated?

A

in a ligand-independent manner by assembly of the pre-TCR complex

151
Q

How has the essential function of the pre-TCR complex in T cell maturation been demonstrated?

A

By numerous studies showing that lack of the TCR β chain, pre-Tα, CD3 or ζ chains results in a block in the maturation of T cells at the double-negative stage

152
Q

In contrast to the TCR β chain locus, there is ____ or __ allelic exclusion in the α chain locus

A

little or no

153
Q

Because there is no allelic exclusion in the α chain locus, productive TCR α rearrangements may occur where?
What can this result in?

A

On both chromosomes, and if this happens, the T cell will express two α chains

154
Q

How many mature peripheral T cells do express two different TCRs, with different α chains but the same β chain?

A

up to 30%

155
Q

It is possible that only one of the two different TCRs participates in what?

A

self MHC-driven positive selection

156
Q

What does unsuccessful rearrangements of the TCR α gene on both chromosomes leads to what?

A

A failure of positive selection and apoptosis

157
Q

Double-positive thymocytes are produced without what?

What do they express?

A

Ag stimulation

They express αβ TCRs with randomly generated specificities

158
Q

What are the only APCs that mediate the positive selection by displaying a variety of self peptides bound to class I and class II MHC molecues

A

Cortical epithelial cells

159
Q

Weak recognition of self peptide-self MHC complexes promotes what for T cells?

A

The survival of the T cells

160
Q

Explain death by neglect

A

Thymocytes whose receptors do not recognize self MHC molecules die by apoptosis

161
Q

What is positive selection involving T cells?

A

Is the process in which thymocytes whose TCRs bind with low avidity to self peptide-self MHC complexes are stimulated to survive

162
Q

What does positive selection ensure?

A

That T cells are self MHC-restricted

163
Q

During the transition from double-positive to single-positive cells, what do thymocytes with class I MHC-restricted TCRs become?

A

CD8+CD4-

164
Q

During the transition from double-positive to single-positive cells, what do thymocytes with class II MHC-restricted TCRs become?

A

CD4+CD8-

165
Q

Double-positive T cells express TCRs that may recognize what?

A

Either self class I or self class II MHC

166
Q

The commitment of immature T cells towards either lineage may depend on what?

A

The random probability of a double-positive cell differentiating into a CD4 or a CD8 T cell

167
Q

A cell that recognizes self class I MHC may randomly differentiate into a CD8 T cell and do what?

A

A CD8 T cell (with the appropriate coreceptor) can survive

168
Q

The same cell that recognizes self class I MHC may randomly differentiate into a CD4 T cell and do what?

A

A CD4 T cell has the wrong coreceptor and may fail to receive survival signals

169
Q

What is a more widely accepted view of how T cells actively induce expression of the correct coreceptor and shut off expression of the other coreceptor?

A

That class I MHC-and class II MHC-restricted TCRs deliver different signals that induce the correct coreceptor

170
Q

It is known that double-positive cells go through a stage at which they express what?

A

High CD4 and low CD8

171
Q

For a class I MHC-restricted cell, when it sees class I MHC, what will happen?

A

It will receive a weak signal because levels of the CD8 coreceptor are low

172
Q

What do weak signals to a class I MHC-restrictied cell that sees a class I MHC activate?

A

Activates Runx3 that maintains the CD8 T cell phenotype by regulating the expression of CD8

173
Q 
For a class II MHC-restricted, when it sees class II MHC, what signals will it receive?
What will these signals activate?
A

It will receive a stronger signal because of high CD4 levels and these strong signals activate GATA3, which commits cells toward a CD4 fate

174
Q

The high-avidity recognition of self Ags triggers what?

A

apoptosis and death resulting in negative selection of the T cell repertoire

175
Q

Both DCs and Mo in the medulla and medullary thymic epithelial cells are what?
What does this process control?

A

APCs that mediate negative selection

Controls the central tolerance to self Ags

176
Q

However, thymocytes high-avidity recognition of self Ags may also differentiate into what?

A

Regulatory T cells that function to prevent autoimmune reactions

177
Q

What does the survival of naive lymphocytes require?

A

Survival signals before they encounter the foreign Ag

178
Q

The same self peptides involved in the selection of double-positive thymocytes in the thymus may be involved in what?

A

The survival in the periphery

179
Q

What may positive selection allow many different T cell clones to do?

A

survive and differentiate

180
Q

Many of the T cells that have positive selection recognize self peptides with (high/low) affinity

A

low

181
Q

Matured T cells strongly recognize foreign Ags and become what?

A

Activated and generate an immune response

182
Q

Recombination of TCR γ and δ loci proceeds in a fashion similar to that of TCR β and α, although the order of rearrangement appears to be what?

A

less rigid

183
Q

In a developing double-negative T cell, rearrangement of TCR β,γ, or δ loci is initiated _______.

A

Simultaneously

184
Q

If a cell first succeeds in productively rearranging its TCR γ as well as its TCR δ before it makes a productive TCR β rearrangement, it is selected into what?

A

the γδ T cell lineage

185
Q

How often do developing double-negative T cells become γδ T cells?

A

10%

186
Q

How often do developing double-negative T cells become αβ T cells?

A

90%

187
Q

Why does the limited diversity of expressed γδ TCRs occur?

A

Because only a few of the available V, D, and J segments are used in mature γδ T cells, for unknown reasons

Immunology Test II (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions