Immunogenetics Flashcards
Ig receptors, TCRs, class I MHCs, CD4s, CD28s, and ICAM-1 are all members of what receptor family?
Immunoglobulin superfamily
What makes up the BCR?
Surface Ig
2 invariant chains (Igalpha and Igbeta)
What roles do the 2 invariant chains Ig-alpha and Ig-beta play in the BCR?
Ensure surface expression of Ig molecule and function in signal transduction
What makes up the TCR complex?
TCR (alpha and beta chains)
2 CD3 complexes (epsilon/gamma and epsilon/delta)
Zeta chains
At what stage in general lymphocyte development is there growth factor-mediated committment, proliferation, and initiation of antigen receptor gene rearrangement?
From Stem –> pro-lymphocyte –> pre-lymphocyte
At what stage in general lymphocyte development does the following occur:
Selection of cells that express pre-antigen receptors as well as reside in generative organ
Pre-lymphocyte
At what stage in general lymphocyte development does the following occur:
Selection of repertoire and acquisition of functional competence
Immature lymphocyte
During hematopoeisis, what is the most important cytokine for the development of the lymphoid cell lineage?
IL-7
What process involves gene rearrangement events occurring in the absence of antigen?
Clonal selection
Allelic exclusion is __________, meaning it occurs for the specific epitope
Monospecific
What are the 3 major mechanisms for generation of lymphocyte receptor diversity?
Combinatorial diversification (somatic recombination)
Junctional diversity
Somatic hypermutation
What mechanism for generation of lymphocyte receptor diversity involves point mutations occurring in fully assembled V-J and V-D-J regions during an immune response?
Somatic hypermutation
What major mechanism for generation of lymphocyte receptor diversity involves addition of nucleotides during the process of D-J or V to D-J joining?
Junctional diversity
What major mechanism for generation of lymphocyte receptor diversity involves V-J or V-D-J recombination of multiple germline genes?
Combinatorial diversification = somatic recombination
True or false: the mechanisms accounting for immune diversity for BCR/antibodies and TCRs are identical
True
In what receptor type does somatic hypermutation occur?
BCRs ONLY, it does not occur in TCRs
The production of which chains in the T cell correspond to the production of the heavy and light chain in the B cell?
Production of heavy chain in B = Beta chain in T
Production of light chain in B = alpha chain in T
During combinatorial diversification, what is the primary difference between heavy and light chains?
Heavy chain has VDJ and C regions
Light chain has VJ and C regions (no D)
[this is the same in TCR - beta chain has VDJC, alpha chain as VJC]
What are the two loci associated with the BCR light chain and what chromosome are they each associated with?
Ig-kappa chain locus = Chr 2
Ig-lambda chain locus = Chr 22
What chromosome is the H chain locus associated with for the BCR?
Chr 14
During combinatorial diversification in BCRs, which chain forms first?
Heavy
During combinatorial diversification of TCRs, which chain forms first?
Beta
The heavy chain of the BCR corresponds to which Ig by default?
IgM (mu)
Combinatorial diversification in BCRs consists of:
Heavy chain: _____ to ______, followed by ______ to _______ rearrangement
D to J, followed by V to DJ rearrangement
What directs the recombination of gene segments in B cells?
Recombination signal sequences (RSS)
What are the 2 major roles of recombination signal sequences during VDJ recombination?
- Provide recognition sites for recognition enzymes that cut and rejoin DNA
- Ensure gene segments are joined in correct order (especially important for heavy chain since there is D region)
What enzyme is responsible for recombining V, D, and J segments?
VDJ recombinase
What genes, made only by lymphocytes, encode for the two necessary components of the VDJ recombinase enzyme?
Recombination activating genes (RAG-1 and RAG-2)
When would RAG-1 and RAG-2 be expressed in B and T cells?
Only during their developmental stages
[once B cell reaches plasma cell status, RAG 1 and 2 will no longer be expressed]
Junctional diversity allows for more diversity in BCR and TCRs; these mechanisms generate diversity in the ____________ region (idiotype)
Hypervariable
Junctional diversity consists of insertion of a series of nucleotides between D and J segments.
This is catalyzed by what enzyme?
terminal deoxyribonucleotidyl transferase (TdT)
TdT catalyzes the random polymerization of nucleotides into DNA without the need for a template.
______ nucleotides are added to asymmetrically cleaved hairpins in a templated manner.
_______ nucleotides are added in a non-templated manner.
P
N
Recombination between VJ and VDJ is not always perfect. Additional diversity is added by _______ that occur in the recombination events taking place, which can lead to _______________.
It is estimated that these inaccuracies can triple the diversity generated by DJ and VDJ joining.
The diversity generated by these mechanisms occurs in the _________ region
Errors; frameshifts
Hypervariable
At what level of the “central dogma” is VDJ recombination occurring?
DNA; once these segments have been spliced together, they are transcribed into the primary mRNA transcript
The beta chain of the TCR is made first; which chromosome is this chain located on?
Chr 7
On which chromosome would you find the human TCR alpha and delta chain loci?
Chr 14
On which chromosome would you find the human TCR gamma chain locus?
Chr 7
What is the “second type” of combinatorial diversity and when does it take place?
Occurs after both receptor chains have been successfully rearranged, transcribed, and translated
The 2 different receptor chains are combined to make the antigen-binding site
In comparing BCRs and TCRs, which one overall has more diversity?
TCR
What is the purpose of adding a surrogate light chain to the completed heavy chain of the BCR prior to continuing its development?
The surrogate light chain allows the surrounding stromal cells to check the structural integrity of the completed heavy chain and determine whether it is able to move forward with development
Also prevents further H chain recombination
At what stage in B cell maturation do you have a complete heavy chain and a surrogate light chain?
Pre-B cell
What type of Ig expression would you see on a mature naive B cell?
IgM and IgD
What CD molecules are associated with Pro-B cells?
CD43
CD19
CD10
CD43 is present on stem cells and throughout most of B cell maturation. When does it cease to be expressed on the B cell?
At the immature B cell stage, once the cell has both heavy and light chains
At what stage in B cell development would you have negative selection (deletion), and possible receptor editing?
Immature B cell stage
At what stage in B cell development would you see alternative splicing of VDJC RNA (primary transcript) to form constant mu and delta mRNA?
Mature B cell stage
Once you have your primary mRNA transcript (after VDJ recombination) in BCRs, in what 2 ways can the pre-mRNA be processed?
Bring the VDJ next to the C-mu gene
Bring the VDJ next to the C-delta gene
The resulting mRNAs have the LVDJ-C__ exons contiguous, and will code for a mu or delta chain
_________ cells assist B cells in developoment and express adhesion molecules and cytokines
Stromal
B-cells and stromal cells interact through what ligand and receptor pair?
VCAM-1 and VLA-4
The initial B cell and stromal cell interaction through VCAM-1 and VLA-4 promotes another interaction between what two factors leading to proliferation?
stem cell factor (SCF) and Kit
Different regions of the thymus are distinguished by the cells present and influence the developmental events of T cells.
_________ _______ is the microenvironment for T cell development.
_______ _______ = outer cortical region
_________= inner cortical region
Thymic stroma
Thymic cortex
Medulla
When does thymic activity peak in humans?
During puberty; declines thereafter
The immature T cells contained within the thymus are called __________, which are embedded in a network of epithelial cells called thymic ________
Thymocytes
Stroma
What HLA classes are expressed by thymocytes?
Both HLA classes!
The thymus is a primary lymph organ involved in production of mature lymphocytes, not antigen presentation.
As such, what is the only route by which progenitor cells enter the thymus and mature T cells leave?
The blood
Pro-T cells leave the bone marrow and enter the thymus to complete their maturation. Where in the thymus are the T cells when they are in the Pro-T and Pre-T stages?
Thymic cortex
Pro-T cells leave the bone marrow and enter the thymus to complete their maturation. Where in the thymus are the T cells when they are in the double positive and single positive stages?
Thymic medulla
What CD markers are found on Stem, Pro-T, and Pre-T cells?
c-kit
CD44
CD25
Once the Pre-T cell reaches the double positive stage, its expression changes from c-kit, CD44, and CD25, to what?
CD4+
CD8+
CD3+
At what stage in T cell development do you have positive or negative selection?
Double positive stage
The pre-T cell contains a surrogate alpha chain, what is this chain called?
pT-alpha
At what points during T cell maturation do you have active proliferation?
Between stem and pro-T
Between Pre-T and Double positive
How does the double positive T cell select for CD8 or CD4 selection?
The TCR will RANDOMLY interact with either an MHC class I or II molecule
How many estimated clones of B and T lymphocytes exist?
10^7
Selection of B and T lymphocytes involves 2 important checkpoints - what is the first checkpoint?
After heavy or beta chain is created (Pre-B cell)
Selection of B and T lymphocytes involves 2 important checkpoints - what is the second checkpoint?
After the light or alpha chain is added (immature B cell)
True or false: checkpoints ensure that only lymphocytes that have successfully completed Ag receptor gene rearrangement are selected to mature, and eliminates potentially harmful self-reactive lymphocytes
True
Selection deletes or functionally inactivates cells that display antigen receptors that are self-reactive.
_________ is acquired by immature B cells that do not become activated when challenged with self-antigen
Tolerance
What happens to an immature B cell in the bone marrow that reacts to a multivalent self-antigen?
Undergoes clonal deletion and apoptosis
What happens to an immature B cell in the bone marrow that reacts to soluble self antigen?
Migrates to periphery and becomes anergic
[anergy = unresponsiveness, mechanism of tolerance]
Which type of immune cell can reverse self-reactivity by undergoing receptor editing?
B cells
[NOTE T cells cannot do this!]
In what developmental stage are B cells able to undergo receptor editing?
Only occurs in developmentally arrested, immature B cells
How does receptor editing occur in developmentally arrested, immature B cells?
After ligation of IgM with self-antigen, RAG protein synthesis remains on for additional rearrangement of light chain genes.
If the new light chain is not reactive with self-antigen, then tolerance is established and the B cell will mature (if it is still self-reactive – will undergo apoptosis)
_______ ________ in B cells assesses the compatibility of receptors produced from successive gene rearrangements
Receptor editing
Double positive thymocytes exist in the cortex and undergo positive selection, meaning only those cells with TCRs that bind appropriately to MHC molecules on ___________ _________ cells survive
Cortical epithelial
As T cells mature, they migrate from the thymic cortex to the thymic medulla. After undergoing positive selection, they undergo negative selection where they are assessed based on encountering self-peptides on _________ cells in the __________
Dendritic
Medulla
What process in T cell maturation establishes self-restriction and recognition of self MHC?
Positive selection
What process in T cell maturation establishes central self-tolerance, meaning T lymphocytes do not become activated by self-antigen?
Negative selection
True or false: after positive selection, thymocytes are self-MHC restricted, but they may still be able to react to self antigen
True
What would be the result of a CD4+ thymocyte reacting weakly to class II MHC + peptide?
Positive selection
What would be the result of a thymocyte having no recognition of self-MHC + peptide?
Failure of positive selection –> apoptosis (death by neglect)
What would be the result of a CD8+ thymocyte reacting weakly to a class I MHC + peptide?
Positive selection
What would be the result of a thymocyte having strong recognition of either class I or class II MHC + peptide?
Negative selection (apoptosis)
_______ cells are a small population of self-reactive CD4+ T cells that function as peripheral suppressors by inhibiting self-reactive Th1 cells in the periphery
Treg
What are the identifiers present on a Treg cell?
CD3+
CD4+
CD25+
What transcription factor is associated with Treg cells?
FoxP3
What is the purpose of “peripheral tolerance”
Not all self Ags are present in the bone marrow or thymus, so the peripheral mechanism evolved to ensure that the mature B and T cells can be tolerated in the periphery if they encounter self Ag
_________ _________ is the process of gene rearrangement of the lymphocyte receptors and the combinatorial association of the receptor chains during development
Clonal selection
True or false: the clonal selection process is antigen-dependent
FALSE - Clonal selection occurs independent of antigen
Clonal selection ensures that lymphocyte clones expressing all of the possible ____________ are produced during development and ________ simply selects those clones which have the appropriate receptor.
The selected clones are then activated, proliferate, and differentiate into lymphocyte ___________ cells.
Specificities
Antigen
Effector
