Unit 2- T Cell Immunity Flashcards
What do T Cells recognise?
degraded proteins bound by MHC molecules
What do B Cells recognise?
recognise native proteins
What is MHC Restriction?
T cell recognise peptide antigens when bound to an MHC molecule- T cells are stimulated only in the presence of an MHC antigen so T cells develop a tolerance to self MHC.
What two signals do T Cells require for activation?
- CD28 molecule on T cells delivers a co-stimulatory signal upon engaging either of its ligands (CD80 or CD86).
- IL-2 cytokine important for T Cell proliferation
What do CD8 T Cells do?
kills target cells that display antigenic fragments of cytosolic proteins (e.g. viruses) bound to MHC Class I molecules
What do CD4 T Cells do?
What two types of T Helper Cells can be produced from this?
recognise antigens in association with MHC Class II.
TH1 or TH2
If TH1 gives an exaggerated response……
a granuloma (aggregation of macrophages) forms
What happens if TH2 is activated?
- antigen recognition induces the expression of CD40 ligands and cytokines by TH2
- TH2 activates B Cell which proliferates and differentiates into plasma cells
What is the immune response to bacteria? (5)
- complement activation (destruction & phagocytes)
- macrophage phagocytosis and activation (TLRs)
- Ig production- making the cell more susceptible to phagocytosis
- T helper activation
- ADCC (Antibody- dependent cell mediated cytotoxicity reactions)
What is the immune response to a Virus? (4)
- Natural Killer Cells
- Macrophage phagocytosis and activation (TLRs)
- Ig Production
- Cytotoxic T Cell activation
What is the immune response to parasites? (6)
- antibody neutralising IgE
- neutrophils
- macrophages
- Cytotoxic CD8 T Cells
- TH2 T Cells, IL-4, IL-5, IL-6
- antibody dependent cell mediated cytotoxicity reactions
In an immune response to a virus, why does the release of cytotoxic T Cells work?
some viruses can prevent their epitope presentation by reducing the expression of MHC class I molecules on the cell membrane- the natural killer cells recognise those with reduced MHC class I molecules on the cell membrane and kill them, suspecting them as virus-infected cells.
Briefly explain the method of adaptive immunity to viruses?
- B Cell binds to virus through viral coat protein
- Virus particle is then internalised and degraded
- Peptides from the virus are presented to the T Cell- the T Cell recognises the processed antigen which activates the B Cell
- Activated B Cell produces antibody against viral coat protein e.g. TH2
What happens if after an adaptive immune response to a virus, the same antigen is seen again?
- Antigen recognition induces the expression of CD40 ligand and cytokines by the TH2 cell
- This activates the B cell which proliferates and differentiates into plasma cells
When are cytotoxic T Cells useful?
when a virus has entered the cell- antibodies such as IgG do not work if inside the cell
What granules does a Cytotoxic T Cell contain? (3)
HINT- granules = toxins
Perforin- ‘punches’ holes in the membrane of the target cell
Granzymes- proteases which trigger a cascade of enzymes leading to programmed cell death
CTL- kill their targets by binding Fas ligand to Fas on target cell- Fas then instructs target cell to apoptise
Briefly describe the neutralising function of IgG?
- Toxin binds to cell- surface receptor
- Endocytosis of toxin receptor complex
- Dissociation of toxin to release active chain which poisons the cell
- Neutralising antibody blocks the binding of toxin to cell surface receptor
Why does Antigenic drift occur? What can it lead to?
results from error prone copying of viral DNA
Can lead to outbreaks of influenza infections
How does Antigenic Drift occur?
- neutralising antibodies against hemagglutinin block binding to cells
- mutations after hemagglutinin epitopes so that neutralising antibody no longer can bind
Briefly describe the method of ADCC (Antibody- dependent cell mediated cytotoxicity reactions)?
- Phagocytosis and breakdown of bacteria by macrophage induces expression of MHC Class II
- Macrophage delivers a co-stimulatory signal to T Cells recognising bacterial peptide antigen
- This leads to the proliferation and differentiation of T cells specific for bacterial protein
How do Bacterial infections lead to the production of a TH2 response?
- B Cell binds bacterial polysaccharide component of vaccine conjugate
- The conjugate is internalised
- peptides from the toxoid are presented to the T cell which activates the B Cell
- Activated B cell differentiates into plasma cell
