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CELL-MEDIATED IMMUNITY, Th cells, CTL, Pathogen on MHC I - CTL, Pathogen …
CELL-MEDIATED IMMUNITY
MEDIATED BY T CELLS
T cells is important to immune system as it can control the intracellular pathogens (viruses) & activate B-cells produced more Abs
Pathogen is normally susceptible to the Abs only in the extracellular environment / blood. When pathogen resides in cells, we need T cells to act on it.
FUNCTIONS
Direct lysis of the infected cells - intracellular microbes (viruses) replicating within infected cells - CTL
Produce Cytokines - activate infected cells (Macrophage) to kill the pathogens/phagocytosed microbes - Th cells
INGREDIENT 1: ANTIGEN
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AG PROCESSING (MHC I)
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Proteins synthesised inside a cell & generally derived from pathogens that have infected a host cell
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CROSS-PRESENTATION
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DC is able to takes up exogenous Ag by either phagocytosis / pinocytosis & present it on MHC I to CD8 T cells
DC is an APC - but it has MHC I as it can generated peptides from exogenous Ag - This explain why APC can has both MHC classes
AG PROCESSING (MHC II)
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Example: Pathogens / Foreign proteins (vaccines) that do not injure the host but activate immune response
The protein is internalized - fuses with endosomal / lysosomal vesicles (highly acidic) - vesicles contained peptides intersect with MHC II vesicle inside cell
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INGREDIENT 2: APC
Cells that able to endocytose Ag, degrade (process) & present (display) Ag fragment on cell surface (MHC protein) to T lymphocytes & activate them
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CLINICAL DISEASES
ROLE OF TH1
Hypersensitivity - Macrophages, CD8+ T cells & NK cells are the principal effector for CMI, they are referred to as delayed type hypersensitivity (type IV). (e.i. contact sensitivity to poison ivy) its Ag activate Langerhans cell which activate Th1 cells to synthesise IFN-γ & other cytokines to recruit & activate macrophages & inflammatory response. Lack of Th1 may lead to severe disease progression; activate autoimmune diseases such as RA & MS
ROLE OF TH2
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Immune Response to parasite (Helminth worm) - Presence of IL4 (by Th2) produce IgE & activation of eosinophils. IgE bind to worm & eosinophils contain granules, the contents is toxic to worm
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ROLE OF CD8 T CELLS
Graft rejection (organ transplantation), kill virally infected cells & tumour cells
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SUPRESSION
Treg (T cells subset) can suppress the function of CD4 & CD8 cells (autoimmune dis & rare x-linked dis
Imbalance in CD4 & CD8 cells - Patient with HIV tend to destroy CD4 cells - Lack of delayed hypersensitivity to M lepray Ag - lack of cellular immunity - excess CD8
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Pathogen on MHC II - Th cells (TH1, TH2, TH17)
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