What recognises abnormal antigens in the innate system?
Pattern Recognition Receptors e.g.:
- PAMPS = detect pathogens antigens e.g. Lipopolysaccharide
- DAMPS = Detect damaged cell antigens e.g. DNA
What triggers inflammation?
PRRs detect PAMPS/DAMPS
- -> Immune cells e.g. macrophages release cytokines (IL-1 & TNF-alpha)
- -> Increased vascular permeability, vascular adhesion molecules and chemokines
Example of a Vascular Adhesion Molecule released in inflammation?
Selectin
How do WCs escape into inflamed tissues?
Leukocyte Extravasation (aka Diapedesis)
What causes the cardinal signs of inflammation (Calor, Rubor, Dolor, tumor)?
Histamine & bradykinin
How are immune cells recruited?
Profesional APCs present antigens to them via MHC2 –> T cell recruitment
What’s the difference between CD8 T cells and NK cells?
NK cells are:
- Faster
- Don’t need antigen priming
- Lack memory
What special cell type can NK cells target?
Infected/damaged cells that lack an MHC1
How does NK cell activation work?
They have both activatory and inhibitory receptors (attach to host MHC1).
to be activated the +ve signal must outweight the -ve.
Activatory receptors also respond to cells lacking an MHC1, hence why NK cells can attack them,
What do NK cells do?
1) Release perforin & granzymes –> Apoptosis
2) Release IFN-gamma –> Macrophages
3) Release TNF-alpha –> Enhanced NK cell cytotoxicity
Describe the process of phagocytosis?
Moves towards infection by chemotaxis
- -> Ingests microbe into phagosome
- -> Phagosome fuses with lysosome to form phagolysosome
- -> Microbe is digested
- -> Waste material formed into residual body and discarded
How does opsonisation hasten phagocytosis?
Reduces -ve charge
And increases binding sites
What are the 3 pathways to activate complement?
1) Classical (Antigen-Ab complex)
2) Lectin
3) Alternative
How does the Lectin pathway work?
Circulating Lectin binds to polysaccharides on the pathogen surface –> Picked up by complement
How does the Alternative Pathway work?
Complement proteins bind to the pathogen surface directly. Without lectin or Abs
How is the complement cascade started?
Activation of C3 Convertase
- -> C3a (Recruits immune cells and mast cells)
- -> C3b (Opsonin, precursor to C5 and helps clear immune complexes)
What complement proteins form the MAC?
C5b, 6, 7, 8 & 9
What does the MAC do?
Punches a pore in the target cell membrane allowing H2O to flow in
- -> Osmotic rupture
- -> Cell Death
