T Lymphocytes PDF

T Lymphocytes  Cell mediated arm of the adaptive immune response  Different populations exist: CD4+ CD8+ Helper T cells Cytotoxic T cells Th1 / Th2/ TFH Tc / CTL T Lymphocytes  1. CD8+ Tc cells:  Cytotoxic and kill cells direc...

T Lymphocytes  Cell mediated arm of the adaptive immune response  Different populations exist: CD4+ CD8+ Helper T cells Cytotoxic T cells Th1 / Th2/ TFH Tc / CTL T Lymphocytes  1. CD8+ Tc cells:  Cytotoxic and kill cells directly.  Respond to pathogens in the cytosol of target cells.  Prevent the spread of infection by inducing programmed cell death (apoptosis). T Lymphocytes  2. Th1 cells  Helper T cells / inflammatory T cells  Activate macrophages and allow uptake of pathogens by phagocytosis  Stimulate production of ROS and NOS  Mediate destruction of pathogens ingested by macrophages. T Lymphocytes  3. Th2 cells  Helper T cells  Mediate anti-parasitic response  Mediate allergic reactions  Activate B cells (provide co-stimulatory signal) T Lymphocytes  What do T cells bind? (TCR Ligands)  Bind to Major Histocompatibility Complex (MHC) proteins.  2 classes of MHC protein - Class I and II  1. Class I are expressed by all nucleated body cells.  CD8+ T cells (Tc) bind MHC Class I proteins T Lymphocytes  2. Class II proteins are expressed by selected immune cells (macrophages, dendritic cells, activated B cells)  CD4+ T cells (Th1/Th2/TFH) bind MHC Class II proteins.  MHC proteins bind to peptide fragments derived from self- and non-self proteins.  These are displayed on the cell surface and T cells recognise them. T Lymphocytes  Class I proteins display peptides from cytosolic proteins.  Class II proteins display peptides from vesicular proteins.  T cells recognise intracellular pathogens, either those infecting a cell directly or those taken up by a cell e.g. macrophage.  In contrast B cells recognise soluble/extracellular pathogens.  Between B and T cells, pathogens in all cellular locations can be recognised. MHC Class I MHC Class II