MCB Lecture 59 Inflammation II Flashcards
What are the different receptors for leukocyte activation?
- 7 pass alpha-helical receptors
- TLR
- Cytokine receptors
- Phagocic receptor
Which cells are important for removal of the cause of inflammation?
Neutrophils
Describe 7 pass alpha helical receptor activation
Chemokines, or other inflammatory mediators act as ligand.
Signal transduction:
Cytoskeletal changes
Increased integrin avidity
Outcome:
Chemotaxis and adhesion to endothelium
Describe TLR signalling in leukocyte recruitment
- PAMPs (such as LPS) bind to the TLR
2a. Production of inflammatory mediators (arachidonic acid, cytokines)
2b. Production of hydrolytic enzymes and ROS
3a. Amplification of inflammation
3b. Killing of microbes
Describe cytokine signalling in leukocyte activation
- Cytokines bind to the membrane bound receptor
2a. Production of inflammatory mediators (arachidonic acid and cytokines)
2b. Production of lysosomal enzymes and ROS
3a. Killing of microbe
3b. Amplification of the immune response
Describe phagocytic receptors role in leukocyte activation
- Opsonised microbe binds to FcR and CR
2a. Production of ROS
2b. Extension of pseudopods, phagocytosis - Killing of microbe
Which are the phagocytic receptors on leukocytes, and what do they bind to?
CR1 and CR2: bind to complement on opsonised bacteria
Fc-gamma-R: bind to IgG on opsonised bacteria
CIq: binds to collectin on microbe
What is opsonisation?
Preparing the microbe for phagocytosis by binding complement and antibody
Describe phagocyte binding to opsonised pathogen
Phagocyte binds via its receptors (CR1 and 2, Fc-gamma-R, CIq) to antibody, C3b and collectin that are bound to the microbe
What are the two modes of phagocytic pathogen killing?
O2 dependent
O2 independent
Describe O2 dependent killing
ROS preoduced in the phagocyte which disrupt the function of the microbe
Which enzymes are involved in O2 dependent killing?
NADPH: O2 -> H2O2
Myeloperoxidase: H2O2 -> HOCl (hydrochlorus radical)
Describe the reactive oxygen species that are formed, and which are the most efficient at killing pathogens that have been phagocytosed
H2O2, not very efficient at killing microbes
HOCl-: very powerful oxidant, good at killing
Peroxynitrate: very powerful oxidant
Describe briefly what O2 independent pathogen killing is
Killing of the bacteria with enzymes released from the granules of leukocytes
What compounds are found in phagocytic granules, and what does each do?
Phospholipase: degrades the microbes’ membrane
Lysozyme: degrades the cell wall
Major basic protein: cytotoxic to parasites
Defensins: puts holes in the cell membrane
Describe how leukocytes can also injury healthy tissue
a. Released toxic products have no distinction between pathogen and host
b. toxic products released when:
- Frustrated phagocytosis
- Regurgitation
- Damage to phagolysosome by ingested irate crystals
Describe broadly how inflammation is regulated
Chemical mediators
What are the two derivations of mediators of inflammation?
Plasma and cell derived
What are the plasma derived enzymatic cascades that regulate inflammation? (3)
- Complement cascade
- Kinins
- Coagulation, fibrinolysis
What is the function of the regulatory enzymatic cascades?
These amplify and coordinate the immune response
Describe the presence of the plasma derived chemical mediators under normal and inflammatory conditions
Normal: present, but inactive
Inflammation: become activated at the site of injury
Describe the complement system
There pathways of activation
Cleavage of C3
Opsonisation, lysis, inflammation
What are the two types of cell derived chemical mediators of inflammation?
Preformed
Newly synthesised
What are the preformed cell derived chemical mediators?
Histamine in leukocyte granules