Week 2 T cells Flashcards
The thymus is a primary or secondary lymphoid organ?
Primary lymphoid organ
What important types of cells are found in the cortex of the thymus?
Cortical epithelial cells, thymocytes (developing lymphocytes)
What important types of cells are found in the medulla of the thymus?
Medullary epithelial cells, dendritic cells and macrophages
How many antigen-binding sites do T cell receptors have?
Just 1
What co-receptor on the T cell surface indicates the rearangement of TCR alpha and beta chains?
CD3
CD4+ T cells are what type? CD8+?
CD4 = Helper T cells, CD 8 = Cytotoxic T cells
What are the stages between stem cells and naive mature T cells?
Stem cell -> Pro-T (double negative, neither CD4 or CD8) -> Pre-T -> Double positive (CD4 + CD8) -> single positive (CD4 or CD8) -> naive mature T cell
What class of MHC are CD4+ cells restricted to? CD8+?
CD4+ -> class II restriction, CD8+ -> class I restriction
What is the role of the zeta chain in T cell receptor signaling?
Zeta chain contains the item sequence which will be phosphorylated, mediating the recruitment of other molecules. The MAP-kinase cascade will be activated, leading to synthesis and activation of transcription factors
Signals induced by TCR complex activation: TCR -> ?, CD28 -> ?, Cytokines -> ?
TCR -> activation, CD28 -> costimulation, Cytokines -> differentiation
What does MHC stand for?
Major Histocompatability Complex
Which cells have MHC class I? Which have class II?
MHC Class I: every nucleated cell, Class II: antigen-presenting cells
What are the most important antigen-presenting cells? What are some less important ones?
Dendritic cells are most important for antigen-presentation, macrophages less so, and neutrophils are most important for phagocytosis but also carry antigen-presentation function. B cells also perform antigen-presentation
Which subunit of Class I MHC molecules binds to CD8+ T cell receptors?
alpha 3
Which subunit of Class II MHC molecules binds to CD4+ T cell receptors?
beta 2
Can T cells ever be activated without MHC recognition?
No! There is MHC restriction
How are antigens presented by MHC class I?
Cytosolic proteins and defective ribosomal products are degraded to peptide fragments, and TAP (transporters associated with antigen processing) delivers those peptides to the ER. The peptide binds the MHC class I molecule and completes its folding, then the MHC class I molecule is exported to the cell membrane
How are antigens presented by MHC class II molecules?
A foreign antigen is endocytosed, then degraded into peptide fragments. Vesicles containing peptides fuse w/ vesicles containing MHC class II molecules
If an antigen enters the bloodstream, where will antigen-presenting cells likely capture it?
In the spleen
What do Helper T cell type 1 do?
Recognize complex of bacterial peptides with MHC class II and release cytokines which activate macrophages, as well as B cells and neutrophils
What do Helper T cell type 2 do?
Recognize complex of antigenic peptide, including multicellular parasites, with MHC class II and release cytokines that lead to activation of B cells into plasma cells
What does thymus-dependent activation mean?
How B cells usually cannot be activated alone, but only with the help of helper T cells
What type of antigens are CD8+ T cells particularly good for?
Virus-infected cells
What effect do the two types of helper T cells have on each other?
They inhibit each other
How to cytotoxic T cells cause apoptosis of target cells?
Granzymes and perforins are exocytosed by the T cell and then endocytosed by the target cell, which then activate apoptotic pathways
What percentage of the mononuclear cells in the blood/spleen are natural killer cells?
5 to 20%
What do the inhibitory receptors of natural killer cells bind to?
MHC class I molecules. NK cells will kill cells without MHC I.
What activates natural killer cells?
Fc-receptors, NKG2D. If there is no MHC I on the surface of a cell, NK cells will kill it
What is DiGeorge syndrome?
congenital malformation affecting development of thymus, leading to T cell deficiency
What is Bare lymphocyte syndrome?
Lack of MHC class II expression, so defective antigen presentation to T cells
What cells are infected by HIV?
CD4+ T cells, macrophages, dendrites
