Inflammation and Repair Flashcards
What are the classical localized signs / symptoms of acute inflammation?
Rubor - redness
Tumor - enlarged area due to edema / swelling
Calor - Warmth
Dolor - Pain
What is one important feature of tissue in order for inflammation to occur?
Tissue must be vascularized in order for cellular / molecular reaction of inflammation to occur (involves vascular response and leukocyte influx)
What is the primary difference between acute / chronic inflammation in terms of cellular involvement?
Acute - involves neutrophils and monocytes from blood converting to macrophages
Chronic - Predominately macrophages, lymphocytes, and plasma cells
When does a repair process typically occur?
Occurs concurrently with acute inflammation but usually finishes afterwards
What is the vascular response of acute inflammation and how does this occur? How does this relate to edema?
- Vessels vasodilate -> increased blood flow + intravascular hydrostatic pressure
- Vascular permeability increases -> protein leaks out into interstitium -> fluid follows -> exudative edema
What leads to the intravascular stasis of blood in inflammation?
Plasma leaks out of the vasculature into the interstitium -> blood becomes thick and sludgy due to the formed elements of the blood being in greater concentration
What chemicals mediate the hyperemia of inflammation? What is their role?
These are the vascular vasodilators:
Histamine and NO
-> increase the intravascular hydrostatic pressure
What are the four mechanisms of how vascular permeability is increased in acute inflammation, and which is most common?
- Formation of gaps between endothelial cells of venules - most common
- Injury to endothelium of microcirculation
- Endothelial transcytosis
- Secondary to angiogenesis - forming blood vessels are immature / leaky
What are the two mechanisms behind forming gaps between endothelial cells? What mediates this?
- Immediate response -> endothelial cell contraction mediated by histamine, bradykinin, and leukotrienes
- Delayed, longer-lasting response -> retraction of endothelium due cytoskeletal changes mediated by cytokines (IL-1, TNF, and IFN-y)
What causes injury to endothelial cells in microcirculation?
Bacterial toxins, tissue necrosis, or activated leukocytes (i.e. macrophages / neutrophils)
What is endothelial transcytosis and how does it occur?
Water can leak THROUGH endothelial cells in a VEGF-mediated phenomenon, occurring mostly in endothelium of venules.
Where and when does leukocyte diapedesis usually occur? What initiates the process?
Occurs in postcapillary venules, with neutrophils entering 1-2 days after injury
Process is initiated when leukocytes are marginated due to the intravascular stasis of blood (not mediated by a receptor)
Where does vasodilation occur? Increased vascular permeability?
Vasodilation - Primarily in pre-capillary arterioles, increases the hydrostatic pressure in the capillaries + venules
Vascular permeability - primarily in the venules, but due to endothelial injury can occur anywhere in vasculature
What are the steps in invasion of leukocytes into the tissues?
- Margination
- Rolling
- Adhesion
- Transmigration (diapedesis)
How does rolling occur? What upregulates this
Leukocytes transiently attach to E-selectins on endothelium in a low affinity interaction to slow them down via their sialylated carbohydrate ligands (sialyl-Lewis) receptors.
E and P selectins are upregulated via histamine, TNF, and IL-1
What mediates adhesion?
Firm attachment, high affinity interaction between VCAM-1 and ICAM-1 (integrin ligands) of endothelial cells and ligands on leukocytes. These are upregulated via IL-1 and TNF.
ICAM = integrin cell adhesion molecule
What process moves integrins to a high-affinity state?
Chemokines from the inflamed tissue (i.e. IL-8) are transcytosed and expressed on interior vascular surface. These also bind to the leukocytes and cause higher affinity expression of ligands on leukocyte surface which bind ICAM/VCAM more tightly
What CD marker mediates diapedesis of leukocytes, and what is needed to get thru the basement membrane?
CD31 - PECAM-1 = “peeking thru the endothelium”
-> collagenases are needed to break through the basement membrane of the endothelium
How does chemotaxis occur?
Exogenous or endogenous chemotaxic factors bind GPCRs on leukocytes, leading to actin reorganization with assembly at the front of the filopod and disassembly at the rear to move towards the stimulus, with contraction of actin / myosin
What receptors can mediate the activation of leukocytes?
- Toll-like receptors
- GPCRs - chemokines and anaphylatoxins
- Cytokines - IFN-y
- Opsonins - IgG, C3b, etc
What occurs once leukocytes are activated? (This can occur in the bloodstream or interstitium)
- Inflammatory response is amplified -> greater adhesion and production / secretion of chemical mediators
- Initiation of phagocytosis and release of toxic products like ROS both intracellularly and extracellular
How does recognition and engulfment in phagocytosis work?
Recognition - via receptors (i.e. TLRs) or opsonins
Engulfment - cytoplasmic pseudopods surround particle, form a phagosome which will be fused with a lysosome
What are the two mechanisms of killing in phagocytosis and which is more important? What mediators are involved in the less important pathway?
- Oxygen-dependent - most important
- Oxygen-independent - less important, includes proteins which increase permeability of membranes, including lysosomes, proteases, hydrolases, defensins, and major basic protein of eosinophils
What are the oxygen-dependent mechanisms of killing?
- Formation of superoxide anion via NADPH oxidase
- Formation of hypochlorite (OCl-) via myeloperoxidase
- Generation of peroxynitrite radicals from NO