Lymphocytes and their receptors - Bittencourt Flashcards
What are the 3 major types of lymphocytes?
T cells
B cells
NK cells
Which cell regulates adaptive immunity and is responsible for cellular immunity?
T cells
What are B cells responsible for?
Antibody production
When does T cell development begin?
Before birth
T cells that express a beta chain become _______
ab T cells (most common)
T cells that express gamma or delta chains become _____
gamma delta T cells - involved in innate and adaptive, less common
ab T cells
most common
involved in adaptive immunity
What part of the immune system do NK cells play a role in?
Mostly innate!!
Does participate in ADCC pathway in adaptive immunity
What segments are found on the beta chain of TCR receptors?
VDJC segments
- Variable region
- Joining region
- Constant region
- Diversity segment
What segments are found on the alpha chain of TCR receptors?
VJC segments
- Variable region
- Joining region
- Constant region
** no diversity segment
What segments are found on both alpha and beta chains on TCR’s?
variable region and constant region
How does TCR gene rearrangement begin?
With rearrangement of beta chain genes in pre-T cells (thymocytes)
How is a ab TCR assembled?
- Beta chain assembled first
- Random joining of Diversity and Joining segments (DJ-beta)
- Random linking of DJ-beta segment with Variable segment (DJV-beta segment)
- Forms variable region of beta chain
Then alpha is assembled!!
- Variable segment and Joining segment make complete alpha chain variable region (VJ- alpha segment)
- VJ-alpha segment then joins with C-alpha region = VJC alpha chain
What is RAG1-RAG2 complex?
Helps with the recombination of VDJ segments
Cleaves the VDJ segments
What does DNA-dependent protein kinase do?
excises the intervening DNA to increase diversity of TCRs
What does terminal deoxynucleotidyl transferase do?
Reconnects V and J segments and adds random nucleotides within a coding joint
Where does selection of T cells take place?
In the thymus - positive and neg selection
What causes thymocytes to undergo apoptosis?
- no TCR present
- Non functional TCR
= apoptosis
What is positive selection of T cells?
a test to see if new TCRs can bind to MHC molecules
only T cells that bind MHC pass positive selection, if not they undergo apoptosis
96% of Thymocytes fail positive selection
Which cells are able to migrate from the thymus?
only non-self-reactive T cells can leave
this avoids autoimmunity
What is the result of T cells that bind STRONGLY to MHC/self antigen complexes on APCs?
Failed negative selection - Apoptosis
What is the role of Autoimmune Regulator gene? (AIRE gene)
enhances negative selection in the thymus, prevents autoimmunity
helps detect self reactive T cells to kill them ASAP
induces expression of antigens found in other tissues of the body
If a thymocyte has high affinity for an MHC II molecule what happens?
The thymocyte that is CD4+/CD8+ will turn off the CD8+ gene and begin to solely express CD4+
If a thymocyte has high affinity for an MHC I molecule what happens?
The thymocyte that is originally CD4+/CD8+ will turn off the CD4+ gene and begin to solely express CD8+
What are the CD4+ Th cells?
Th1, Th2, Th17, Treg
Where are B cells produced?
In bone marrow
Who has more receptors, T cells or B cells?
B cells
How many binding sites do B cells have? T cells?
B cells have 2 binding sites
T cells have 1 binding site
How many polypeptide chains are on a BCR?
4 polypeptide chains
- 2 identical heavy chains
- 2 identical light chains
A constant and variable region in each chain
What segments are found on the heavy chain of BCRs?
VDJ segments
- Variable segment
- Diversity segment
- Joining segment
What segments are found on the light chain of BCRs?
VJC segments
- Variable segment
- Joining segment
- Constant segment
What determines the type of heavy chain on BCR?
constant segment
What is first to appear on pro-B cells?
Heavy chains D and J
- Diversity and Joining
How are BCRs assembled?
Heavy chain assembled first
- D and J segment join
- V segment joins DJ segment = VDJ segment
- alpha and beta Poly-Ig chains join
Then light chain forms
- V and J segments join = VJ segment
When are light chains rearranged?
at the pre-B cell stage
what Igs are found on a mature B cell?
IgM and IgD
but IgD has no function
What occurs if a immature b cell is stimulated?
leads to cell death or anergy, state of no response
When is a B cell at full maturity?
When IgD is expressed with IgM on the surface of the B cell
Which chain on a BCR contains a diversity segment?
only the HEAVY chain
How are B cells eliminated?
Through negative selection or clonal deletion
