Exam III: Inflammation Part II Flashcards
Plasma Protein Derived Mediators
Three interrelated systems: complement, kinin, and clotting systems
Complement System: General Information
Consists of more than 20 proteins numbered C1 through C9
Functions in both innate and adaptive immunity for defense against microbial pathogens
Several cleavage products of complement proteins are elaborated
Causes increased vascular permeability, chemotaxis, and opsonization
Critical step in complement activation= proteolysis of the third (and most abundant) component, C3
Complement System: Inflammation
Inflammation
C3a, C5a, and, to a lesser extent, C4a are cleavage products of the corresponding complement
Stimulate histamine release from mast cells to increase vascular permeability and cause vasodilation
C3a, C5a, and C4a are called anaphylatoxins
C5a: powerful chemotactic agent for neutrophils, monocytes, eosinophils, and basophils
Activates the lipoxygenase pathway of AA metabolism in neutrophils and monocytes
Causes further release of inflammatory mediators
Complement System: Phagocytosis
Phagocytosis
C3b and its cleavage product iC3b (inactive C3b)
When fixed to a microbial cell wall, act as opsonins
Promote phagocytosis by neutrophils and macrophages
Complement System: Cell Lysis
Cell lysis
Deposition of the MAC on cells causing the cells permeable to water and ions resulting in death (lysis) of the cells
C3a and C5a
Most important inflammatory mediators
Can be cleaved by several proteolytic enzymes present within the inflammatory exudate including plasmin and lysosomal enzymes released from neutrophils, which initiate a self-perpetuating cycle of neutrophil recruitment
Directly self perpetuate the inflammatory process
Complement Activation and Effector Functions
Alternative Pathway (microbe triggered), Classical Pathway (Ab triggered), and Lectin Pathway (mannose binding lectin triggered) converge at the step where C3b is deposited on the microbe causing the following effector functions:
- C3a and C5a causes inflammation
- C3b/C3bi causes phagocytosis
- Formation of MAC causes lysis of microbes
Coagulation and Kinin Systems
Culminate in the activation of thrombin and the formation of fibrin
Intrinsic Clotting Pathway
Series of plasma proteins activated by Hageman factor (factor XII), which is a protein synthesized by the liver that circulates in an inactive form and activated upon contact with negatively charged surfaces
initiated by chemicals released from platelets and collagen, which activates 12a, 11a, 9a, 10a, 2a/thrombin, 1a/fibrin, and stabilized fibrin (activated in that order)
Kinin
Vasoactive peptides derived from plasma proteins (kininogens)
Action of specific proteases (kallikreins)
Active form of factor XII (factor XIIa)
Converts plasma prekallikrein into an active proteolytic form (kallikrein) and cleaves a plasma glycoprotein precursor high-molecular-weight kininogen, to produce bradykinin
Bradykinin
Increases vascular permeability Causes contraction of smooth muscle Dilation of blood vessels Pain when injected into the skin Short-lived---quickly inactivated by an enzyme called kininase
Fibrinolytic System
At the same time factor XIIa is inducing fibrin clot formation, it activates the fibrinolytic system
Cascade counterbalances clotting by cleaving fibrin
Solubilizing the clot
Kallikrein: cleaves plasminogen, which is a plasma protein that binds to the evolving fibrin clot to generate plasmin and a multifunctional protease
Fibrinolytic system: primary function of plasmin that lyses fibrin clots
Cleaves the complement protein C3 to produce C3 fragments
Degrades fibrin to form fibrin split products
Activate Hageman factor to trigger multiple cascades
Summary of Mediators
Bradykinin, C3a, and C5a: mediators of increased vascular permeability
C5a: mediator of chemotaxis
Thrombin: effects on endothelial cells and many other cell types
C3a and C5a
C3a and C5a: generated by several types of reactions
Immunologic reactions, involving antibodies and complement (the classical pathway)
Activation of the alternative and lectin complement pathways by microbes, in the absence of antibodies
Agents not directly related to immune responses
Plasmin, kallikrein, and some serine proteases
Activated Hageman Factor
Activated Hageman factor (factor XIIa): initiates four systems (inflammatory response)
- Kinin system: produces vasoactive kinins
- Clotting system: induces formation of thrombin
- Fibrinolytic system: produces plasmin and degrades fibrin to produce fibrinopeptides
- Complement system: produces anaphylatoxins and other mediators
Morphologic Hallmarks of Acute Inflammation
Morphologic hallmarks of acute inflammation:
Dilation of small blood vessels= increased permeability
Slowing of blood flow
Accumulation of leukocytes and fluid in extravascular tissue
Serous Inflammation
Marked by outpouring of thin fluid
Derived from plasma/secretions of mesothelial cells
Peritoneal, pleural, and pericardial cavities
Accumulation of fluid in these cavities= effusion
Skin blister: burn or viral infection causing a large accumulation of serous fluid
Examples of Serous Inflammation
Serous effusion of the right pleural cavity – clear, straw colored fluid meaning you can see through it and it is yellowish
Chylous effusion of the peritoneal cavity meaning that it is lymphatic fluid- either a rupture of lymphatic vessel
Blood in the pleural cavity – hemothorax NOT a pleural effusion
Fibrous Inflammation
Fibrinous exudate
Vascular leaks are large
Local procoagulant stimulus (e.g., cancer cells)
Characteristic of inflammation: lining of body cavities like the meninges, pericardium and pleura
Microscopic examination: fibrin appears as an eosinophilic (very pink) meshwork of threads (dropped butter example)
Amorphous coagulum
Removed by fibrinolysis and clearing of other debris by macrophages
Consequences of Fibrin not Removed
If fibrin is not removed: stimulates ingrowth of fibroblasts and blood vessels and leads to scarring
Conversion of the fibrinous exudate to scar tissue (organization)
Pericardial sac: opaque fibrous thickening of the pericardium and epicardium and obliteration of the pericardial space and affect heart beat