immuno chapter 7.txt
Card Set Information
immuno chapter 7.txt
Immuno chapter 7
T cell progenitor cells leave before gene rearrangement can occur
positive and negative selection
Peripheral lymphoid orgasns
encounter foreign antigens and are activated
Migration to active sites
activated t cells migrate to site of infection to activate macrophages or kill host cells or b cell area
Path of t cells
Born in bone marrow, travel to thymus to develop, once matured they circulate the secondary lymphoid tissues
Why is the thymus a primary lymphoid tissue?
it is only involved in development, not directly fighting infection
What does the thymus contain?
Thymocytes (immature T cells) and t cells, macrophages, dendritic cells, and thymic stroma (epithelial cell)
thymic epithelium does not develop so there is no thymus
Outer, close packed and consists of ECTOdermal cells; contain thymocytes and macrophages
Inner, less dense consists of endodermal cells; contains theymocytes, dendritic cells, and macrophages
Thymic anlage (early thymus)
the combination of the ectodermal cells early in development that is later colonized by progenitor cells from the bone marrow
replacement of thymus tissue with fat tissue after puberty
What occurs in the early stage of development?
progenitor stem cells enter the thymus but do not have t cell markers
stem cells persist in the thymus and start to aquire the correct receptors, adhesion molecules and signaling molecules (IL-7 is secreted by thymic stromal cells and helps develop t cells)
begin to rearrange TCR genes
have t cell characteristics but no CD4, CD8, CD3, or TCR
secreted by thymic stromal cells and binds to IL-7 receptor on CD34+ cells
Notch 1 receptor
on thymocytes; binds to ligands on thymic epithelial cells
What signals do IL-7 and notch 1 initiate?
they result in the removal of repressive transcription factors
What occurs in the middle stage?
TCR gene rearrangement starts for DN thymocyte;Becomes a DP thymocyte when CD4 and CD8 are expressed due to beta rearrangement.
pTalpha holds the beta chain in place
What composes the pre-TCR
pTalpha and beta
What does the pre-TCR signal
the termination of arrangement
What is the first checkpoint?
to determine if the beta chain has the potential to bind to alpha chains
What happens if the pre-TCR passes the checkpoint?
it becomes a pre-T cell
beta chain has how many chances to rearrange
What happens with successful beta rearrangment?
pre-TCR formation and RAG shut down
What segments does the alpha chain have?
V and J; has many j segments so successful rearrangment is likely
what is excised during alpha rearrangment?
What happens when the alpha chain is successfully rearranged?
it pairs with the beta chain and shuts down RAG
Developing T cells that recognize self will be positively selected
developing t cells that bind too tightly to self will be negatively selected
What is the end result of positive and negative selection?
t cells will bind to self moderately well
Single positive thymocyte
positive selection determines if a T cell will become CD4 or CD8 depending on which MHC it binds
Regulatory T cells
CD4 t cell that binds self antigens and suppresses other CD4 T cells that can bind to the same APC
Are there more CD4 or CD8 cells?
twice as many CD4
Bone marrow transplant
GHD occurs when mature t cells from the donor attack the host
Host immune system attacks transplanted organ if rejected
Tumor therapy- select, enrich and amplify TILs