T cells Flashcards
Where do T cells come from?
Arise from bone marrow, but mature in the thymus
general location of T cells
circulate in the blood in length
what are T-cell receptors
They are antibody like receptors on the surface of T cells, which specialize in recognizing protein agents presented by MHC
number of T cells in the body
300 billon
killer T cells / cytotoxic T lymphocytes (CTLs)
- activated by MHC I being presented on cells (done by MOST cells)
- connects to the target cell
- convinces/triggers target (infected APC) to commit suicide
helper T cells
- activated by MHC II on APC
- secretes cytokines: IL-2, IFN-γ
Regulatory T cells
- keep the immune system from overreacting
- much is unknown about them
what is needed for T cells to function?
They must be activated
types of APCs that activate helper T cells
- activated dendritic cells
- activated macrophage
- activated B cells
requirements for activation
- TCR protein (α, β) for antigen
- Co-receptor proteins (CD4 or CD8) for MHC recognition
- Co-stimulatory molecules (B7 proteins)
- CD3 or four proteins (γ,δ, ε and ζ) for signaling
T-cell recognition occurs when
Occurs when the TCR recognizes its cognate antigen
T cell Receptors (TCR)
molecules on surface of T cell
- TCR only recognize peptides presented by MHC I or II
- Not diverse
- All TCRs on mature T cells are IDENTICAL
- Types: traditional (95%) = αβ Or non-traditional (5%) = γδ
T cell selection/maturation process
- If T cells sees “self” being presented by other cells, then the T cell commits suicide b/c it must be able to distinquish what is “self-made”
- If T cell recognizes “self” antigen, but does NOT get co-stimulation, it is rendered inactivated (anergized) and will eventually die. This processes is called “peripheral tolerance”
- If T cell sees non-self AND gets co-stimulated, it will be ACTIVATED
Non-traditional T cells
- They express γδ T cell receptors
- Abundant in intestine, uterus and tongue
- Less diversity than αβ receptor, thus more effective at recognizing protein fragments from invaders
- Less is known about this type
Recognition requires
- TCR (α, β)
- Co-receptor (CD4 or CD8)
Co-receptor
Either CD8 or CD4 on the T cell which recognizes MHC (I or II respectively)
- When T cells are in the thymus, they express both CD8 and CD4
- As T cell matures, one type of co-receptor is down regulated