Expressed on all T cells and is needed as a signal transducer for the T cell receptor
peptides are generated from larger polypeptides
CD8 T Cell
directly attack virus infected cell
recognize MHC I
CD4 T Cells
helper T cells
T helper 1 - recognize macrophages
T helper 2 - recognize B cells
recognize MHC II
control T cell mediated immune responses
determine the fate of transplanted tissues
HLA molecules encoded in MHC
MHC I cells
almost all nucleated cells
excluding brain and erythrocytes
process antigens from INSIDE the cell
MHC II cells
antigen presenting cells
take up antigens from OUTSIDE cell
How are MHC genes inherited?
genes are co-dominant
a given T cell receptor will recognize its peptide antigen only when the peptide is bound to a particular form of MHC molecule.
T cell maturation
Start with double negative progenitor cell (lacks CD4 and CD8)
End with double positive CD3+
Weak recognition of MHC I/II + peptide by immature T cell
determines expression of either the CD4 or CD8 molecule
Death by neglect
Immature T-cell does not recognize MHC + peptide
Immature T cell binds too strongly to MHC + peptide
allows lymphocytes to home to lymph nodes or to sites on infection
Allows T cells to "talk" to APCs
T cell activation and signal transduction
PKC activates transcription factor NKfB
Calcineurin activates transcription factor NFAT
NKfB & NFAT start production of cytokines
CD80 and CD86
molecules on APC that binds CD28 on naive t cells and deliver necessary co-stimulatory signal to t cell
delivers required second signal for T cell activation
1) Binding of TcR and CD4 to MHC class II delivers signal to T cell.
2) Clonal expansion of T cell can occur only after second signal is delivered by CD80/86:CD28 interaction.
down regulated by CTLA4
Source: Th1 cells
Effect: T cell growth
IL4 and IL5
Source: Th2 cells
Effects: antibody production, class switching
Source: Th2 (Treg)
Effects: inhibits Th1
EffectL inhibits Th2
CD8 T cell effector molecules
Perforin, granzymes, fas
CD4 T cell effector molecules
Response: down regulates Th1, inflammatory, humoral
T-helper 1 cells
Driven by IL12 and IFN-gamma
Host defense against intracellular microbes
Cellular immunity (CD8 T cells, macrophages)
T-helper 2 cells
Driven by IL4
Produce IL4, 5, 10, 13 and TGF-ß
host defense against helminths
Humoral Immunity (B cells)
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