BIOL 2050U Lecture Notes - Thymus, Ctla-4, Glycoprotein

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30 Jan 2013
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LYMPHOCYTE ACTIVATION
all immune system responses begin with NAÏVE T CELL ACTIVATION
features of T-cell activation that are distinct from other receptor-ligand processes
requires MHC-presentation
small proportion of T cells can respond to ANY antigen
many different MHC-peptide combinations are presented by a single APC
self-reactivity is a concern
Naive T-cell activation causes their DIFFERENTIATION
CD8+ cells respond to MHC class I indicates viral infection
activation causes diffentiation into CYTOTOXIC T CELLS
CD4+ cells respond to MHC class II indicates microbial infection
activation causes differentiation into TH1 or TH2 cells
TH1 – inflammatory response (macrophage mediated)
TH2 – antigenic response (B-cell mediated)
T CELL COSTIMULATION –
signal 1 = antigen-MHC
signal 2 = antigen independent costimulatory signal (B7)
**ensures that only APC’s can cause T-cell differentiation**
APC’s:
DC’s – MOST important activator of T-cells; presentS viral antigens
Macrophages – present bacterial antigens
B cells – present bacterial and viral antigens
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