L13: Inflammatory Response Flashcards
Hallmarks of the inflammatory response
rubor (redness)
tumor (swelling)
calor (heat at tissue site)
dolor (pain)
functio laesa (loss of function)
Inflammation is caused by ______.
vascular changes:
- endothelium leaks
- edema
- positive feedback loop of cell signaling
- further changes in cell adhesion molecules on both cells and endothelium.
Giving blood is associated with _____ (as are statins, aspirin and fish oils, all of which are anti-inflammatory and all of which tend to increase bleeding).
lower heart disease
generally used to describe a variety of molecules used to identify pathogens. The first group identifies was the toll-like receptors, but many more types.
-PAMPS (pattern-associated molecular proteins)
-molecules that are normal cell components but should be inside
– cytoplasmic or nuclear proteins of membrane proteins belonging in the inner leaflet.
DAMPS (death or damage-associated molecular proteins)
Response to PAMPS and DAMPS =
- Activate complement, which in turn releases inflammatory signals (anaphylatoxins)
- Attracts neutrophils, macrophages and mast cells.
- Smallish (90 to 130 amino acids), with conserved cysteines
- Receptors are seven-span membrane proteins.
- Binding activates G-proteins
Inflammatory Chemokines
Cross reception common: a given chemokine may bind more than one receptor and a specific receptor may bind more than one chemokine
G-proteins kick of several internal cascades:
- hydrolyzes membrane phospholipids to IP3 and DAG -lets Ca2+ loose in the cytoplasm, polymerizing actin and promoting movement
- kicks off Ras cascade that leads to activation of transcription factors.
The High-endothelial Venules are found __
at the end of capillaries in lymph nodes, Peyr’s patches, and tonsils (not spleen).
In the HEV rhe endothelial lining here is composed of cells that ___
do not look like flattened paving stones, but are thicker.
Most lymph cells that extravasate attach to these specific cells in the ____
HEV
The HEVs specifically attract ____ and do NOT attract neutrophils
lymphocytes
The HEV develops in response to _____.
foreign antigen exposure
-you don’t see this in mice raised in a germ-free environment and you don’t see this in tissues that have the circulation to them blocked to that antigen does not enter.
The unique morphology of the HEV is associated with ___
the induced expression of specific selectins, mucin-like, and Ig CAMs, and they specifically allow different classes of lymphocytes to home to different organs and regions of the body.
Cell adhesion molecules involved in extravasation:
Selectins, mucins, I-CAM, integrins
- membrane glycoprotein with lectin at amino terminus that binds carbohydrates. Compare with complement lectin pathway
- specific for sialic acid (mucins have a lot of these)
- comes is L (Leukocyte), E and P (endothelium) versions
- initiate initial sticking of leukocytes to the endothelial wall
Selectin family
- protein part rich in serine and threonine (OH-containing R groups)
- LOTS of carbohydrate linked to these OHs.
- Carbohydrates have lots of sialic acid, interact with selectins
Mucin-like family
-The mucin-like versions of the endothelium interact with the selectins on the leukocytes and vice-versa.
- endothelium has several versions
- mucosa has another, which also has a mucin-like domain
- bind to integrin on leukocytes
- inflammation increases their expression
I-CAM- Ig superfamily
- Heterodimer (α and β chains)
- Expressed in leukocytes -Different integrins bind to different immunoglobulin CAMs (cell specificity)
- Can also bind to fibronectin
- Cytoplasmic portion can interact with cytoskeleton and signaling proteins such as the tyrosine kinases, Fyn and Lck.
Integrin family
4 steps of extravasation
- rolling
- activation
- arrest and adhesion
- transendothelial migration
Rolling
- attachment by low affinity P selectins (yellow) on the endothelium to mucin-like molecules on the neutrophil (purple).
- Because the connections are loose, they tend to break and the neutrophils kind of roll along, attaching to one endothelial cell after the next as it is swept along by the flow of blood.
Activation
- the “stick and release” from the rolling response along the endothelium triggers chemokine (IL-8) release by the endothelium.
- The neutrophils activate G-protein cytoplasmic pathways via the 7-span receptor.
Steps of arrest and adhesion
1) The chemokine binds to a 7-span chemokine receptor.
2) This receptor activates a G protein and sets off an internal signaling cascade.
3) The integrins change conformation, enter the lipid rafts, deploy and stick Ig tightly to the Ig CAMs of the endothelium
4) Some of the first proteins affected are those that associated with the inner side of the plasma membrane and connect to the cytoskeleton
Transendothelial migration
- the arrested neutrophil then finds the gap between two adjacent endothelial cells and squeezes through it.
- The cytoskeletal changes lead to the neutrophils changing shape and moving by amoeboid motion.
- The neutrophil forms a leading wedge and ootches through a gap between the endothelial cells (recall that inflammation makes the endothelium somewhat leaky).
____ for example are attracted by inflammatory signals and cruise into sites of active infection, where they may be activated by antigen presented by innate cells fighting the infection.
T cells
____ may also be activated by dendritic cells in the lymph nodes in spleen. In that case the dendritic cells also communicate the site of the infection by activating specific T-cell surface receptors for cytokines and CAMs characteristic of particular tissues. For example retinal/retinoic acid is produced by the gut and only gut-homing T cells have receptors for it. For skin, it’s vitamin D.
T cells
____ tend to head to the site of infection.
Effector cells
____ tend to head to the tissues that initially had the infection.
Memory cells
Inflammatory cytokines
IL-1, IL-18
- The signals are smallish proteins with β-pleated sheets.
- Synthesized as precursor in the cytosol, then clipped and secreted: leaderless secreted proteins.
- Most members activate TH17 cells, although an inhibitory version exists as well.
IL-1
- Synthesized in the cytosol, clipped and secreted.
- Production of precursor under different controls.
- Activate TH1 responses.
- Promote IFN-γ production, which in turn promotes its secretion in a positive feedback loop.
IL-18
Release of IL-1 subtypes and IL-18 are in turn promoted by activation of ____. Along with complement activation, the signaling that leads to IL-1 and IL-18 release is part of the very first responses to a new infection.
pattern-recognition receptors
Examples of PRRs:
- LPS (lipopolysaccharide) activation of TLRs – recall that these TLRs are transmembrane proteins with a cytoplasmic domain that kicks off a complex pathway to NFκB and AP-1 activation, which in turn up-regulate genes for inflammatory cytokines: IL-1, IL-18, IL-6 and TNF α.
- NOD receptors (members of a group of NLR proteins with annoying complex naming conventions) are in the cytoplasm, recognize viral, bacterial parasite signatures using a leucine-rich repeat domain, as well as DAMPS and environmental irritants. Also activate NFκB and AP-1 and thus inflammatory cytokines.
Secondary danger signals that result in assembly of inflammasome after initial activation of PRRs…
- Pathogenic signatures – wide variety of proteins, nucleic acids and cell wall components from bacteria, virus, fungi and protozoa.
- Environmental irritants- alum (used as a vaccine adjuvant), inorganic particles (asbestos, silica, metals), UV light.
- Internal signals- ATP and glucose, crystals of cholesterol and urate, β-amyloid, hyaluronin.
This picture represents the
Assembly of the inflammasome
What activates the inflammasome?
Caspase 1 hydrolysis
Consequences of activated inflammasome:
caspase-1 cleaves IL-1 precursor
- part goes to nucleus
- part is secreted from cytoplasm
The inflammasome is similiar in structure to the ____
apoptosome
Similarities between apoptosome and inflammasome:
- wheel-like structures, typically seven units
- homologies in regions of the axis/assembly
- activated by leucine rich ligand binding domains
- have CARD (caspase recruitment) domains at axis
- bind caspases via their corresponding CARD domains
- Caspases active hydrolytic domains at axel region
- Caspases then clip effector proteins
Differences between apotosome and inflammasome:
Inflammatory mediators include:
Clotting, kinins, lipid derivatives
Clotting:
- Clotting both up-regulates, and is up-regulated by, inflammation. This is why chronic inflammation can lead to strokes and cardiac infarcts.
- Initiated by platelets and RBCs contacting damages surfaces (collagen fibrils) and breaking open.
- This releases and activates Hageman factor, with several consequences.
- The clotting cascade ends with prothrombin activation, which clips fibrinogen into fibrin and peptides.
- The fibrin forms the clot.
- The released peptides promote inflammation.
- Hageman’s factor also activates the fibrinolytic system, which dismantles the clot using the enzyme plasmin.
- Plasmin also produces inflammatory peptides and activates complement
Kinins
- Specifically leads to pain, in addition to increased endothelial permeability and smooth muscle contraction.
- Cascade initiated by Hageman factor.
- Also involve proteolysis.
- Leads to clipping of kininogen to bradykinin. (ACE inhibitors)
Lipid derivatives
-Membrane phospholipids play a structural role but also serve as the raw material for generating a lot of signaling compounds.
- Arachidonic acid- derived from one to the fatty acids.
- Act on it with enzymes called cyclooxygenases (COX2 inhibitors) and you can get
- thromboxane
- prostaglandins
- Act on it with lipoxygenase and get a variety of leukotrienes.
- In a separate origin pathway, phospholipids can provide the raw material for Lyso-PAF, which is converted to PAF (Platelet Activating Factor)
IFNγ and TNFα, transcription factor NF-κB are associated with __
chronic inflammatory response
Anti-inflammatory treatments
- antibodies used to block luekocyte extravasation
- corticosteroids
- NSAIDs
- Cooling
Antibodies used to block leukocyte extravasation
antibodies to integrins
antibodies to CAMS
corticosteroids
- Prednisone, cortisone, dihydrocortisone
- High doses block adrenals and many immune functions
- Side effects – mood swings, edema, glaucoma, increased susceptibility to infections
NSAIDs
- Aspirin (acetylsalicylic acid), Advil (ibuprofen) Aleve (naproxin) are OTC
- prevent prostaglandin production from arachidonic acid. Celebrex specifically blocks COX-2
- NOT Tylenol/acetaminophen- acts on brain to raise pain threshold and lower hypothalamic thermostat).
Cooling
- Interferes with inflammatory process (recall that fever is often a helpful part of the response to infection)
- used to prevent excessive tissue damage following injury or stroke- exercise raises levels of CRP and other inflammatory indicators
- used during surgery
- used to cut down on symptoms of autoimmune disease multiple sclerosis – chilling via hands to allow athletic competition.
- Harmful if you’re ill, unless your fever is dangerously high.
