Simple theory exam notes from these pictures
CELL MEDIATED IMMUNE RESPONSE
- (a) Cytotoxic T-cell (Tc cell)
- (b) NK cells
- (c) ADCC (NK cells, Macrophages, Neutrophils, Eosinophils)
(a) Cytotoxic T-cell (Tc / CD8+ T-cell)
- Processed Ag loaded on MHC-I of APC / any nucleated cell binds to TCR of CD8 T-cell (Tc cell)
- CD28 of Tc cell binds to B7 of APC (co-stimulatory signal)
- Cytokine signal - IL-2 from T_H1
- Tc cell gets activated → cytosolic tail of CD8 molecule has tyrosine kinase activity
- Causes phosphorylation of tyrosine residues of ITAM (Immunoreceptor Tyrosine Based Activation Motif)
- ITAM now acts as docking site for ZAP-70
- ZAP-70 (Zeta Associated Protein Kinase) becomes active → generates multiple intracellular signals
- Gene expression:
- Perforins - Produce pores in target cell membrane
- Granzymes - Enter through pores and induce APOPTOSIS of the cell
(b) NK Cells
- Non-MHC restricted cells, no memory
- Markers: CD16, CD56, CD99
- Kill tumor cells & virus-infected cells
| Step | Event |
|---|---|
| 1 | Tumor/virus-infected cells show reduced MHC-I expression |
| 2 | Inhibitory signal to NK cell is lost |
| 3 | NK cells recognise ligands on such cells via activation receptors (CD16) |
| 4 | NK cells activated → secrete Perforins & Granzymes |
| 5 | Apoptosis of target cell |
- Normal cells express MHC-I normally
- NK cell receptors bind MHC-I → causes inhibitory signal → suppresses NK cell activity
(c) ADCC - Antibody Dependent Cellular Cytotoxicity
- Virus-infected cells are coated by Fab portion of IgG immunoglobulins
- Effector cells (NK cell / Macrophage / Eosinophil / Neutrophil) bind to the Fc portion of IgG via their Fc receptors
- Cells get activated and release cytotoxic factors:
| Cell | Cytotoxic Factor |
|---|---|
| NK cells | Perforins & Granzymes |
| Neutrophils | Lytic enzymes |
| Eosinophils | Perforins & Lytic enzymes |
| Macrophages | Lytic enzymes |
- → Lysis of the cell
- ZAP-70 = Zeta Associated Protein Kinase
- ITAM = Immunoreceptor Tyrosine Based Activation Motif
- CD8 T-cells are MHC-I restricted; NK cells are non-MHC restricted
- Both Tc cells and NK cells kill via Perforins + Granzymes
- ADCC uses antibody (IgG) to guide cellular killing
Make flashcards for exam prep on immune mechanisms
A set of 4 exam flashcards on "Cell Mediated Immune Response" arranged in a 2x2 grid on a clean white background. Each card has a dark blue header with white question text and a light background answer section. Card 1 - Q: "What are the 3 mechanisms of Cell Mediated Immunity?" A: "a) Cytotoxic T-cell (Tc), b) NK cells, c) ADCC (NK cells, Macrophages, Neutrophils, Eosinophils)". Card 2 - Q: "What is ITAM and its role?" A: "ITAM = Immunoreceptor Tyrosine Based Activation Motif. After Tc activation, tyrosine residues of ITAM get phosphorylated → becomes docking site for ZAP-70". Card 3 - Q: "How does Cytotoxic T-cell kill a target cell?" A: "MHC-I + Ag → TCR binding + CD28-B7 co-stimulation + IL-2 → ZAP-70 activation → Perforins (pores) + Granzymes → Apoptosis". Card 4 - Q: "What is ZAP-70?" A: "Zeta Associated Protein Kinase. Docks to phosphorylated ITAM → generates multiple intracellular signals → gene expression of Perforins & Granzymes"
A set of 4 exam flashcards on "NK Cells and ADCC" arranged in a 2x2 grid on a clean white background. Each card has a deep green header with white question text and a light background answer section. Card 1 - Q: "NK cell markers and key features?" A: "Markers: CD16, CD56, CD99. Features: Non-MHC restricted, No memory, Kill tumor & virus-infected cells". Card 2 - Q: "Why don't NK cells kill normal cells?" A: "Normal cells express MHC-I normally → NK cell receptor binds MHC-I → Inhibitory signal generated → NK cell suppressed". Card 3 - Q: "How do NK cells kill tumor/virus-infected cells?" A: "Reduced MHC-I on target → Inhibitory signal lost → CD16 activation receptor recognises ligands → Perforins & Granzymes secreted → Apoptosis". Card 4 - Q: "What is ADCC and which cells mediate it?" A: "Antibody Dependent Cellular Cytotoxicity. Mediated by: NK cells (Perforins+Granzymes), Neutrophils (Lytic enzymes), Eosinophils (Perforins+Lytic enzymes), Macrophages (Lytic enzymes)"