• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/92

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

92 Cards in this Set

  • Front
  • Back
describe the two different TCR's expressed by T-cells?
1. alpha/beta receptors
2. gamma/delta receptors
T cells that leave the thymus are restricted to those that express what?
Self MCH (the MCH I and II that are expressed by that person)
what is the first selection process through which the primary T-cell repertoire must undergo?
positive selection for those that can bind self MCH I and II isoforms
what is positive selection for T cells followed by?
negative selection in which those T cells which bind too tightly to MCH are killed
the majority of T cells have which receptor type?
alpha/beta
what are the immature T cells located in the thymus called?
thymocytes
where are the thymocytes located?
in a network of epithelial cells called the thymic stroma
the epithelial cells of the cortex are derived from?
ectoderm
the epithelial cells of the medulla are derived from?
endoderm
the epithelial cells from the cortex and medulla together form the?
thymic anlage
the progenitor cells from the bone marrow that infiltrate the thymic anlage give rise to what two cell types?
1. thymocytes
2. dendritic cells
what other cell besides the progenitor cells comes to the thymus from the bone marrow?
macrophages
where are the macrophages primarily located in the thymus?
the medulla
As the thymocytes mature describe their direction of migration?
from cortex to medulla
what is the phrase that refers to the degeneration of the thymus after puberty?
involution of the thymus
What is the effect of removing the thymus in an adult?
Nothing really happens becuase peripheral T cells are long lived and can self renew
where do the progenitor cells from the bone marrow go to once the enter the thymus?
in the subcapsular region of the outer cortex
what signals the progenitor cells to proliferate in the thymus?
interaction with the stromal cells (epithelial cell network)
what do the resulting cells of progenitor proliferation display on their cell surface?
CD2
the cells expressing only CD2 and neither CD4 or CD8 are called?
double negative thymocytes
as the double negative thymocytes mature, describe the series of cell surface molecules they express?
first CD44 (adhesion molecule) then CD25 (component of IL2 receptor)
what determines whether a T cell will be a alpha/beta or gamma/delta?
whichever can make a productive rearrangement first wins
what is the major difference between the determination of the order of TCR loci rearrangement and BCR rearrangement?
TCR gene loci all begin rearrangement at the same time while BCR gene loci proceed in a series
what must happen for the a T cell to choose to have alpha/beta receptors?
the beta-chain rearrangement must by productive before both gamma and delta chains
which usually has a faster productive rearrangement, beta chains or the gamma/delta chains?
the beta chains
once a productive beta chain is assembled, how is a pre-T cell receptor made?
beta chain is joined with a surrogate alpha chain
the presence of the pre-T cell receptor on the T cell surface causes what to happen with chain rearrangement?
it stops all chain rearrangment and the cells begin to proliferate
after proliferation of T cells expressing pre-T cell receptors, what occurs?
recombination machinery is expressed again and alpha, gamme, and delta chains all begin rearrangement
what occurs if gamma/delta chains make a productive rearrangement before the alpha chain does?
the T cell will express gamma/delta receptors instead of alpha/beta
what does the rearrangement of the alpha chain locus mean for delta chain rearrangement?
the delta chain gene loci is in the alpha chain so rearrangement of the alpha chain deletes delta gene loci from the chromosome
how many thymocytes fail to make productive rearrangements?
98%
what happens to the thymocytes which have not made a productive rearrangement?
they are all phagocytized by macrophages in the outer cortex
which immunoglobulin gene loci is most similar to beta chain loci?
the B cell heavy chain gene loci (VJD regions)
which immunoglobulin gene loci is most similar to alpha chain loci?
the B cell light chain gene loci (VJ regions)
what are the recombination activation genes that are activated before alpha/beta gene loci rearrangement?
RAG-1 and RAG-2 just like B cells
describe all of the components of the pre-T cell receptor? (4)
1. beta chain
2. surrogate alpha chain called the preTalpha
3. CD3 protiens
4. zeta chain
describe the two ways in which an unproductive rearrangement on the beta chain locus can be saved?
1. a productive rearrangement on the beta chain locus on the second chromosome
2. a second, productive rearrangement on the same beta chain locus
how is it possible for a second rearrangement on the same beta chain locus to occur?
two copies of the DJC regions exist in tandem with the V region thus if one is messed up it can be skipped an the other used
what percent of T cells have a productive rearrangement of the beta chain?
80%
succesful rearrangement of the beta chain causes the expression of what two co-receptors on the cell surface?
CD4 and CD8
once the thymocyte expresses CD4 and CD8 it is called what?
a double-positive thymocyte
where are a double-positive thymocyte primarily found?
inner cortex
why does no rearrangement occur during cell proliferation initiated by pre-T cell receptor expression?
RAG-1 and RAG-2 genes are shut down
which has a greater chance of productive rearrangement, beta chains or alpha chains?
alpha chains because like light chains of B cells, alpha chains can have several succesive gene rearrangments
why can alpha chains undergo more gene rearrangements that beta chains?
alpha chains have more V and J (over 50) gene segments which can be combined
how is it possible for a T cell to express two different receptors?
each T cell has two copies of alpha chain genes thus two productive rearrangements are possible and can be displayed simultaneously
receptors do the first T cells in embryonic development display?
gamma/delta receptors
what is the first phase of T cell production?
to make productive rearrangements leading to functioning TCR's regardless of antigenic specificity
what is the second phase of T cell development?
determination if a TCR, that has been produced in the first phase, has the ability to recognize self-MCH presenting self-peptides and MCH presenting pathogen-derived peptides
how many of the TCR's made in phase one are able to recognize self-MCH?
2%
what is the name given to the process by which only a small population of T cells are able to bind self-MCH and thus survive?
positive selection
what happens to the T cells which fail positive selection?
the die and are phagocytized by mcarophages in the thmyic cortex
where does positive selection take place?
thymic cortex
what present the self-MCH with peptide from normal healthy cells to the double positive T lymphocytes?
cortical epithelial cells
what are the cortical epithelial cells derived from?
ectoderm
describe the time frame in which double positive T lymphocytes must bind self-MCH with self-peptides before apoptosis is initiated?
3-4 days
describe what a bone marrow donor and a bone marrow recipient must share in common for a bone marrow graft to be succesful
the must share AT LEAST 1 HLA class I MCH and 1 HLA class II MCH
other than selecting T cells which can interact the self-MCH, what else does positive selection do for T cells?
selects whether they will express CD4 or CD8
at the end of positive selection, what are thymocytes called?
single-positive thymocytes
which MCH class does CD4 react with?
MCH II
which MCH class doe CD8 react with?
MCH I
how does a CD4 or CD8 get to be the only co-receptor expressed?
positive selection brings the thymocytes into contact with MCH class I or II. Whichever class it contacts determines the co-receptor displayed (CD4 or CD8)
what is the name of the disorder in which either MCH class I or class II is not expressed?
bare lymphocyte syndrome
If a patient with bare lymphocyte syndrome is missing MCH class II what co-receptor will all the T cells express?
CD8
what is the process called by which T cells which bind too tightly to self-MCH and self-peptide are destroyed?
negative selection
which cells are most important in facilitating negative selection for T cells?
bone marrow derived macrophages and dendritic cells
how do the macrophages and dendritic cells help in negative selection?
present thymic antigen to T cells and those T cells that bind too tightly are induced to undergo apoptosis
the negative selection mediated in the thymus can only select for T cells not overly reactive to what?
thymic self-peptides
what process ensures that T cells reactive to self-peptides other than thymic self-peptides do not stay in circulation?
a mechanism very similar to that of B cells in that T cells which bind soluble self-antigens become anergic
what does HLA (as in HLA MCH II) stand for?
human leukocyte antigen
in the absence of antigen, how long to naive T cells circulate through the body?
years
describe the circulation pathway of both B cells and T cells?
blood -> secondary lympoid tissue -> lymph -> blood
what provokes the final phases of developmen and differentiation in naive T cells?
binding of their specific antigen in T cell rich areas of lymphoid tissue
once activated by antigen CD8 T cells become?
cytotoxic T cells
once activated by antigen CD4 T cells become?
TH1 or TH2 cells
what is the aproximate ratio of CD4 T cells to CD8 T cells in the peripheral circulation?
2:1
patients which aids see a drop in what kind of T cells in peripheral circulation?
CD4 T cells
additional MCH molecules expressed by an individual results in deletion of T cells equal to the ___ of the additional MCH molecules expressed?
square
what is the maximum of different MHC molecules that humans express?
12 (3 per MHC Class = 6) (6 times 2 chromosomes = 12)
how many stages are there for T cell development?
4
what is the first T cell developmental stage?
proliferation and differentiation to double-positive CD3 thymocytes
what is the second T cell developmental stage?
positive selection
what is the third T cell developmental stage?
negative selection
what is the fourth T cell developmental stage?
entry to the circulation
what are the thymocytes entering the first stage of T cell development called?
double-negative thymocytes
where are the thymocytes entering stage 1 located?
subcapsulary zone
what are the thymocytes entering the second stage of T cell development called?
double-positive thymocytes
where are the thymocytes entering stage 2 located?
thymic cortex
what are the thymocytes entering the third stage of T cell development called?
double-positive thymocytes
where are the thymocytes entering stage 2 located?
throughout the cortex, but concentrated mostly at the cortico-medullary junction
what are the thymocytes leaving the fourth stage of T cell development called?
Mature single-positive CD4 or CD8 T cells
where do cells which have passed stage 4 leave the thymus?
blood venules