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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
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
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
T-helper 1 cells
Driven by IL12 and IFN-gamma
Host defense against intracellular microbes
Cellular immunity (CD8 T cells, macrophages)
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