Acute inflammation Flashcards
what is inflammation?
Inflammation is the response of the body’s vascularized tissues to harmful stimuli such as infectious agents, mechanical damage, chemical irritants, etc. Inflammation has both local and systemic manifestations and may be either acute or chronic.
is inflammation protective?
Yes.
Protective response intended to eliminate the initial cause of cell injury and the necrotic cells and tissues arising from the injury
- May be harmful
Inflammation is intimately associated with the repair process. True/False
True
what are the objectives of inflammation?
- Localize and eliminate the causative agent
- Limit tissue injury
- Begin the process of healing
what are the causes of inflammation?
- Infectious agents
- Physical agents
- Chemical agents
- Immune reactions
- Necrotic tissue
describe acute inflammation
Acute inflammation is an immediate response to a pathogenic factor (e.g., trauma or infection) and has the following features:
Rapid onset (occurs minutes to hours after an encounter with a causative factor)
Transient and typically short-lasting (provided it is not caused by an immunological condition)
Involves the innate immune system
Characterized by five classic signs of inflammation, which are caused by the release of inflammatory mediators
what are the 5 classic signs of inflammation?
The five classic signs of acute local inflammation are redness (rubor), swelling (tumor), heat (calor), pain (dolor), and loss of function (functio laesa).
define chronic inflammation
- Chronic local inflammation is due to nondegradable pathogens, prolonged exposure to toxic pathogens, or autoimmune reactions.
- Cells involved: mononuclear cells (monocytes, macrophages, lymphocytes, plasma cells), fibroblasts
- Leads to necrosis and fibrosis (simultaneous destruction and formation of new tissue)
- May last for months to years
- The mechanism involves two ways of activating macrophages
1) Classical (proinflammatory): mediated by Th1 cells secreting IFN-γ
2) Alternative (anti-inflammatory): mediated by Th2 cells secreting IL-4 and IL-13 - Outcomes
1) Scarring
2) Amyloidosis
3) Neoplasia (e.g., chronic HCV infection → chronic hepatitis → hepatocellular carcinoma)
what are the outcomes of chronic inflammation?
1) Scarring
2) Amyloidosis
3) Neoplasia (e.g., chronic HCV infection → chronic hepatitis → hepatocellular carcinoma)
2 ways of macrophage activation during chronic inflammation?
1) Classical (proinflammatory): mediated by Th1 cells secreting IFN-γ
2) Alternative (anti-inflammatory): mediated by Th2 cells secreting IL-4 and IL-13
what cells are involved in chronic inflammation?
mononuclear cells (monocytes, macrophages, lymphocytes, plasma cells), fibroblasts
what is the aim of acute inflammation?
The aim is to get the neutrophils to the site of injury as fast as possible to eliminate pathogen or clear necrotic debris
what are the components of acute inflammation?
- Vasodilatation
- Endothelial permeability
- Extravasation of neutrophils
what are the 2 major events of acute inflammation?
vascular and cellular response
describe vascular and cellular response of acute inflammation
vascular response: vasodialtion and icnreased vascular permeability
cellular response:extravasation of neutrophils
what are the sequence of events of acute inflammation?
1) local hemodynamic changes (vasoconstriction → vasodilation)
2) Increase in vascular permeability
3) Extravasation of leukocytes
4) Phagocytosis and killing of the phagocytosed pathogen or lysis of the phagocytosed particles
5) Outcome of inflammatory response
what is the reason of pain seen with acute inflammation?
Stimulation of free nerve endings by certain mediators and H+
Prolonged stimulation → sensitization of ion channels (e.g., TRPV1) → hyperalgesia
what are the mediators of pain seen with acute inflammation?
Bradykinin
PGE2
what is the reason for swelling seen with acute inflammation
Release of mediators from immune cells and endothelium or damage to endothelium → separation of endothelial junctions → separation of endothelial cells → ↑ vascular permeability and ↑ paracellular movement of fluid → leakage of protein-rich fluid to the interstitial tissue → ↑ oncotic tissue in the interstitium → accumulation of fluid in the interstitium
what are the mediators for swelling seen with acute inflammation
Histamine
Leukotrienes (C4, D4, T4)
Serotonin
what is the mechanism of heat and redness seen with acute inflammation?
Release of vasoactive mediators by immune cells and endothelium → vasodilation → ↑ blood flow
what are the mediators of heat and redness?
Histamine
Bradykinin
Prostaglandins (PGE2, PGD2, and PGF2)
NO
describe the vascular event of acute inflammation?
- Vasoconstriction- transient (few seconds)
- Vasodilatation
- Increased vascular permeabilityà exudation of protein-rich fluid
- loss of fluidà concentration of red cells and increased viscosityà blood stasis
what are the sources of mediators released during acute inflammation?
1) Histamine—Basophils, platelets, mast cells
2) Serotonin–Platelets
3) Prostaglandins (PGE2, PGD2, and PGF2)–Leukocytes, platelets, endothelial cells
4) Bradykinin –Plasma
5) NO–Endothelial cells
what is the reason for increased vascular permeability?
•Increased hydrostatic pressure •decrease in intravascular osmotic pressure •Changes in endothelial cells -Endothelial cell contraction -Junctional retraction -Endothelial injury
how endothelial cell contraction occur?
Due to the action of inflammatory mediators (histamine, serotonin, bradykinin, leukotrienes C4, D4, and T4)
Occurs rapidly and does not last long
Results in the opening of interendothelial spaces and paracellular leakage of plasma
during acute inflammation, hydrostatic pressure decrease inside the vessel. True/False
False.
Vasodilatationà increased blood flowà increased hydrostatic pressure
increase hydrostatic pressure result in the development of exudate or transudate?
transduate-ultrafiltrate blood plasma (contains little protein
what happens with osmotic pressure inside the vessel during acute inflammation?
it decreases due to loss of protein-rich fluid, whereas osmotic pressure in interstitial tissue increases.
exudate or transudate is the characteristic fluid of acute inflammation?
exudate (protein-rich fluid) due to Leads to leakage of plasma content into the interstitial tissue
compare exudate and transudate
1)Transudate Extravascular fluid with low protein concentration Specific gravity < 1.012 Hydrostatic imbalance 2)Exudate Extravascular fluid with high protein concentration and cellular debris Specific gravity > 1.020 Alteration in vascular permeability
alteration in vascular permeability result in transudate formation. True/False
False.
Leakage of protein-rich fluid through pores of the vessel–exudate
describe the cellular response of acute inflammation
Within inflamed tissue, leukocytes (mainly neutrophils in early infection) interact with the vascular endothelium and leave the blood vessels to migrate to the site of infection. The process of neutrophil extravasation from the blood to the inflamed tissue occurs in 5 steps:
- margination
- rolling
- adhesion
- diapedesis
- migration.
what are the main effector cells of acute inflammation
1) macrophages
2) neutrophils
3) lymphocytes
4) NK cells
neutrophils
describe the margination
- Leucocytes moving from the centre of the vessel towards the periphery
- Normal flow - RBC’s and WBC’s flow in the centre of the vessel
- A cell poor plasma is flowing adjacent to endothelium
As blood flow slows, WBC’s collect along the endothelium à Margination
what are the 2 mechanisms of margination?
The two main mechanisms that allow for margination are rouleaux formation and dilation of post-capillary venules
what is rouleaux formation?
An aggregation of erythrocytes with the appearance of a stack of coins on peripheral blood smear. This aggregation is caused by increased concentrations of plasma proteins (e.g., fibrinogen, immunoglobulins).
The liver releases increased amounts of fibrinogen (an acute-phase protein) in response to cytokines released by macrophages, monocytes, and other cells near the site of inflammation.
Increased fibrinogen → rouleaux formation → neutrophils are pushed against endothelium of the venules
what is endothelial activation?
The underlying stimulus causes a release of mediators which activate the endothelium causing selectins and other mediators to be moved quickly to the surface
describe rolling
- Neutrophils bounce or roll along with the endothelial cells
- Transiently adhere to endothelial cells
- mediated by selectins molecules (transiently bind to their receptors)
rolling is mediated by what molecules?
1)On endothelial cells
–P-selectin: stored and released from Weibel-Palade bodies within the endothelium in response to inflammation
Release is mediated by histamine.
–E-selectin: released in response to inflammatory mediators, such as TNF and IL-1
–Other: GlyCAM-1, CD34
2)On leukocytes
-Neutrophils and other leukocytes express Sialyl-LewisX and L-selectin, respectively.
These molecules transiently bind to and dissociate from endothelial selectins, allowing leukocytes to roll along the vascular wall
describe adhesion
Leukocytes firmly adhere to endothelial cells
leukocyte adhesion is mediated by…
by integrins, ICAM-1 and VCAM-1.
1) On endothelial cells
- -Intercellular adhesion molecule (ICAM, also called CD54)
- -Vascular adhesion molecule (VCAM, also called CD106)
- -Both upregulated by TNF and IL-1
2) On neutrophils and lymphocytes
- -Neutrophils: β2-integrin (lymphocyte function-associated antigen-1, LFA-1, composed of CD18 and CD11a) → binds to ICAM
- -Lymphocytes and monocytes: β1-integrin → binds to VCAM
- -Expression of integrins is activated by leukotriene B4 (LTB4) and C5a
what is transmigration (diapedesis?)
Movement of leukocytes through the blood vessel wall to the interstitium
Neutrophils release type IV collagenase, which dissolves the basement membrane and allows them to exit the interstitial space.
transmigration is mediated by?
Requires expression of platelet endothelial cell adhesion molecule-1 (PECAM-1, also called CD31) on neutrophils, endothelial cells, and platelets
what is chemotaxis (migration)?
The process by which leukocytes move to the cite of inflammation after leaving the blood vessels
list common chemoattractants
- Leukotrienes: e.g., LTB4
- Platelet-activating factor (PAF)
- Chemokines: e.g., IL-8
- Kallikrein
- Complement fragments: e.g., C5a
- Bacterial products
what are toll-like receptors? (TLR)
Pattern recognition receptors that bind to pathogen-associated molecular patterns (PAMPs)
Activate the NF-κB pathway
what is opsonization?
A process by which pathogens and immune complexes are marked with an opsonin (e.g., complement factor C3b) for phagocytosis, after which the pathogen can be eliminated by phagocytes that express opsonin receptors, e.g., Fc receptor and complement receptor 1.
what are the common opsonins?
C3b
immunoglobulins