Pathophysiology: Inflammation

Why is there an emphasis on the vascularized feature of inflammation?

It indicates that it occurs in the tissues and organs that are vascularized/perfused with blood.

What are the mechanical and chemical barriers (natural barriers)?

Mechanical: ridding the body of pathogens includes sloughing, sneezing, coughing, vomiting, urinating and cilial action of the respiratory tract. As well as low skin temperatures to discourage growth of bacteria. Chemical: includes mucous, perspiration, saliva, tears and earwax that trap and kill microorganisms. Some of these contain enzymes, fatty and lactic acids and antimicrobial proteins that destroy bacteria. Similarly our own body flora is capable of producing chemicals to keep pathogens at bay.

What three events occur usually simultaneously in order to accomplish the goals of inflammation?

1. Increase metabolic rate: cells step up their usual daily routines and increase production of the necessary items for battle. As result we increase our heat production, oxygen and glucose consumption and our production of wastes. 2. Dilation of blood vessels to help speed up delivery of inflammatory components to site of injury. 3. Increased capillary permeability which allows movement of white cells (neutrophils), proteins and nutrients out of the blood vessels and into the tissue where they can go to work.

What are the 5 goals of inflammation?

1. movement of all necessary blood and cellular components to the site of injury or insult. 2. delivery of nutrients and blood cells to eradicate the offender. 3. dilution, confinement and elimination of offending agents. 4. stimulation and facilitation of components to the immune system. 5. promotion of healing with generation of new tissue.

Describe platelets.

Also called thrombocytes and they circulate passively until activated by products of tissue degradation like collagen, thrombin and platelet activating factor. Their role is one of hemostasis, or the stemming of blood flow. Once activated they produce a potent inflammatory mediator which results in increased vascular permeability, chemotaxis, adhesive and proteolytic properties of the endothelium.

Describe eosinophils.

Are granulocytes with many lysosomes. Contain biochemical mediators of inflammation and are especially prominent in allergic response and hypersensitivity disorders. As well, they are particularly good at tackling parasitic infections. Like their counterparts, eosinophils circulate in the blood until needed. They then migrate to tissue where they modulate release of inflammatory mediators and degrade vasoactive molecules, controlling the vascular effects of histamine and serotonin.

There are 3 interrelated plasma protein systems that normally exist in an inactive state. What are they?

Complement, clotting and kinin. Each has it's own end goal. The plasma derived mediators of inflammation are synthesized in liver and include coagulation factors and complement proteins. Many of these protein components are enzymes that circulate in an inactive or "proenzyme" state. Activation of a proenzyme by infection or injury creates a cascade type effect. Components of these plasma protein systems are usually short lived and rapidly deactivated.

Cell derived mediators of inflammation.

Inflammatory mediators are responsible for the wide variety of clinical manifestations seen with the inflammatory response. In normal state, mediators are held within intracellular granules to be secreted at a time when body is in need of protection. We are also capable of synthesizing additional mediators based upon need. The major sources of mediators are platelets, neutrophils, monocytes and macrophages and mast cells, endothelial cells, smooth muscle, fibroblasts and most epithelial cells. Most short lived as they are inactivated by enzymes, scavenged or degraded.

Emigration of Leukocytes.

Initially, leukocytes are recruited to site of injury and facilitated to linger there, by slowing of blood flow. They then line up and move along the endothelial wall and adhere to it with help of adhesion molecules, some of the adhesion molecules are selectins, integrins and members of Ig superfamily like ICAM-1 ICAM2 and VCAM-1-->and are found on both the leukocyte and endothelial cell walls and are complementary, meaning they fit together like lock and key. Then through process called chemotaxis, leukocytes are encouraged to move into tissue where injury.

Nitric Oxide

Produced by endothelial cells and causes smooth muscle relaxation and antagonizes platelet adhesion, aggregation and degranulation. Also plays role in regulating recruitment of leukocytes. Blocking of NO promotes leukocyte rolling and adhesion to capillary venues; delivery of NO reduced leukocyte recruitment, production of NO is implicated in the inflammatory changes associated with atherosclerosis and also some antimicrobial properties.

Thromboxane A2

Produced primarily by platelets at the site of injury and promotes platelet aggregation, bronchoconstriction and vasoconstriction.

Inflammation can be ________: also called the immune response or __________: the inflammatory response.

specific and non-specific

• Examples of chemical mediators that bind to endothelial cells to cause retraction include histamine, bradykinin, leukotrienes etc. • When mediated bind to receptors on the endothelial cells, the cells begin to retract, leaving wide gaps between them. As result, proteins and molecules that were once too big to squeeze between the endothelial cells, can now leave the vessel quite freely, taking water along with them. Loss of water into the extravascular space leads to decrease in osmotic pressure within the blood vessel and edema of the tissues. The individual will also experience discomfort and quite possibly, impaired function. Also with loss of fluid from intravascular space, comes increased blood viscosity. The blood becomes thick and sluggish leading to slower flow. Now the leukocytes are much more able to stick to the endothelium and prepare to leave the area to travel to the site of injury.

yep yep

Inflammation and atherosclerosis

• Recall the normal endothelium that we looked at earlier. Remember that the junctions between endothelial cells are normally right. With injury or elevated cholesterol (esp the low density lipoprotein), monocytes become sticky and attach to the endothelium in response to adhesion molecule expression. As a result, the endothelium begins to produce far less antithrombotic and vasodilating cytokines. Inflammatory cytokines and growth factors are released and monocytes begin to move into the endothelium and platelets become activated. Macrophages form from monocytes and free radicals are released. LDLs are then oxidized. Macrophages consume LDLs, transforming them into foam cells. Foam cells release growth factors and cytokines that further the process of atherogenesis. • Meanwhile, there is a fair bit of communication between the innate and adaptive immune responses. Normally antigen-processing cells of the immune system patrol the environment looking for foreign invaders. When found, these cells process and present them to other cells of the immune system • Upon presentation of an antigen, cells of the immune system develop a lineage of cells that are specific to the antigen and then multiply. Both the T cells and B cells are involved • T cells communicate with the innate immune system and some cells are able to destroy the antigen. B cells give rise to antibodies that are specific to the antigen when signaled to do so by the T cells. • With endothelial injury, the subendothelium is exposed to blood components and platelets adhere and aggregate at the site of injury. This is followed by smooth muscle proliferation. • Smooth muscle proliferation causes the endothelial layer to pouch out, making the lumen of the vessel smaller • As lipids continue to accumulate beneath the endothelial layer, a hard lipid core is formed • Lymphocytes send a signal to the smooth muscle cells to halt formation of collage. At the same time there is an overexpression of enzymes that begin to eat away at the protective fibrous cap • Atherosclerotic plaques are now considered to be unstable or vulnerable as they rupture or fissure, encouraging formation of an occlusive thrombus • Lesions become complicated once they begin to fissure or rupture. Signals are then produced that encourage formation of prothrombogenic mediators. Blood flowing over the lesion is filled with platelets that adhere to the lesion, and aided by expression of procoagulant factors, a thrombus is formed.

What are the 3 possible avenues through which complement cascade can be activated?

1. Classical pathway is activated by antibodies and requires at least two antigen antibody complexes to initiate the cascade. Thus immune system can take advantage of this option for destruction of bacteria. 2. The lectin pathway is activated by bacterial carbs and is similar to classical but no antibodies required. 3. The alternative pathway is activated by gram negative bacterial and fungal cell wall polysaccharides (termed endotoxins); no antibodies required. It begins with activation of C3b and merges with classical pathway at C5. The complement cascade is activated in 3 ways and has 4 major effects: opsonization, mast cell degranulation through anaphylatoxic activity, leukocyte chemotaxis, and cell lysis.

Chemotaxis

A response involving cell orientation of cell movement that is either toward (positive chemotaxis) or away from (negative chemotaxis) a chemical stimulus. When leukocytes leave the capillary, they move in response to a chemical gradient caused by chemokines, bacterial and cellular debris and protein fragments derived from the complement system. Both immune and non-immune cells ensure that leukocytes move in the appropriate direction. Chemotactic factors, also called chemoattractants, cause directional movement of cells toward the site of injury. E.g., include neutrophil chemotactic factor and eosinophil chemotactic factor and these are both contained in mast cells.

Describe acute inflammation.

A response to injury/insult that occurs early and quick (minutes to hours). Any number of stimuli can trigger this response and it is mediated by many factors. It does not last very long and is self-limiting. One key feature is it's non-specificity (ex. if you stub your toe and cut your finger another time the same process will occur regardless of the cause). Two phases of inflammation "vascular" and "cellular". Acute inflammation has 1 of 2 outcomes: healing or chronic inflammation.

Chronic inflammation

After a two week period, the inflammatory process is now considered chronic as opposed to acute. Some organisms (mycobacteria in TB) have waxy cell walls that are not well phagocytized (so inflammatory persists). Other organism (leprosy, syphilis, and brucellosis) can survive within macrophages (TB). Others release tissue toxic chemicals upon their death. Granulomatous inflammation is characterized by infiltration of lymphocytes and macrophages- body isolates the side and walls it off. Granuloma is encapsulated by fibrous deposits and can become calcified. Some of these infections include listeria, brucella, histoplasmosis, and parasitic infections like schistosomiasis, toxoplasmosis, etc.

Describe the complement system.

Components of the complement system include 20 different proteins labeled C1 though C9 and make up about 10% of the total circulating proteins in the body. They are capable of direct or indirect destruction of pathogens or can activate and work with other components of the inflammatory response to effect the same results. As proenzymes are activated, a cascade forms that plays an important role in immunity and inflammation. Complement fragments contribute to the inflammatory response by causing vasodilation, increasing vascular permeability and enhancing activity of phagocyte. C3 and C5 activation is the most important piece of this cascade: activation of C3 and C5 results in formation of opsonins, chemotactic factors and anaphylatoxins (opsonins coat bacteria and tag them for destruction). The most potent component is C3b. Chemotactic factors draw other important inflammatory mediators to the site of injury as needed. Analphylatoxins cause rapid degranulation of mast cells. The most potent one is C3a. C5a has both chemotactic and anaphylatoxic properties. Other important components are C2b which causes vasodilation and increased permeability by smooth muscle relaxation and C4a which also acts as an anaphylatoxin inducing mast cell degranulation with release of histamine. The final endpoint of complement cascade is formation of the membrane attack complex which is composed of C5 through C9. Its job is to create holes in membranes of pathogens allowing entry of water causing cells to explode.

What are the local manifestations of inflammation? Describe each one.

Heat: caused by vasodilation and increased movement of blood to site. Redness: vasodilation and increased movement of blood to site. Edema: vasodilation, increased movement of blood to site, increased capillary permeability leakage of proteins and cells out of the endothelial wall taking water with it; results in increased fluid in tissues. Pain: increase fluid of tissues causes pain; as well prostaglandins act directly on nerve ending to cause pain. Pus: as neutrophils die off, their contents become exudate (pus). Clot: initiation of clotting cascade: acts to sequester invaders in area. Loss of function: may be due to edema and pain.

Arachadonic metabolites

Fatty acids found in phospholipids of the cell membrane. They are released from mast cells and initiate complex reactions that lead to production of other inflammatory mediators (prostaglandins and leukotrienes).

Platelet activating factor

Generated from lipids stored in the cell membrane and induce platelet aggregation. Also serves to activate neutrophils and potentially act as a chemoattractant for eosinophils.

Margination

Leukocytes move along the endothelial wall.

Transmigration

Leukocytes move to site of injury in response to chemotactic factors.

Adhesion

Leukocytes stick to endothelium with help of adhesion molecules.

Describe endothelial cells.

Line the walls of blood vessels and normally maintain very close contact with each other (space very tight to limit movement of cells and particles across the vessel wall). They also produce anti-platelet and antithrombotic agents to prevent formation of clots, produce both vasoconstrictors and vasodilators to regulate flow, regulate leukocyte extravastion through use of adhesion molecules, regulate immune cell proliferation through secretion of colony-stimulating factors, and participate in the repair process through angiogenesis and formation of extracellular matrix.

Describe monocyte/macrophages.

Monocytes are also leukocytes derived from bone marrow but contain larger and fewer lysosomes than their counterparts. They too express receptors that interact with a variety of substances. Typically monocytes exit the circulation in response to inflammation and take up residence in various tissues as the more mature macrophage (monocytes are an immature form of macrophages). Macrophages are named according to their tissue location some examples are Kupffer cells in liver, alveolar macrophages in the lungs. They arrive at the site of inflammation a little later than neutrophils (24-48 hrs post). Eventually they replace neutrophils as they die off. They are often associated with chronic inflammation as they are somewhat sluggish. They differ from neutrophils in other ways too. They produce very potent vasoactive mediators (prostaglandins, leukotrienes, platelet activating factor, inflammatory cytokines and growth factor) and they engulf more material than neutrophils. Their lifespan is 3-4x longer than neuts and they also interact with immune system. Macrophages are responsive to lymphokines from T cells which enhance their efficiency and work with immune system by processing and presenting antigens to the lymphocytes and by stimulating growth and differentiation of granulocytes and monocytes in the bone marrow and substances that promote wound healing.

Describe mast cells.

Most important activators of inflammatory response, by performing two functions: degranulation and synthesis of mediators. They located in connective tissue, close to a blood vessel and are prevalent along the mucosa of lung and GI tract and dermis of skin. They derived from the same hemopoeitic stem cells as basophils but they don't mature until they leave circulation and settle in nearby tissues. They produce lipid mediators and cytokines that induce inflammation. They contain within their cytoplasm, some preformed granules. When activated they release their granular contents (histamine, serotonin, chemotactic factors, enzymes, proteoglycans, proteases, and cytokines such as TNF-alpha and IL-6) into circulation and exert effects immediately. Also synthesize lipid mediators from cell membrane precursors such as prostaglandins and platelet activating factor and stimulate cytokine and chemokine (leukotrienes) synthesis by other cells such as monocytes and macrophages. They are especially important in hypersensitivity and allergies. They bind to one of the immune globulins IgE to trigger the release of histamine and vasoactive substance from basophils. They are also responsible for release of eosinophil chemotactic factor A (ECF-A) which serves to attract eosinophils to site of inflammation.

Oxygen free radicals

Often released by leukocytes after exposure to microbes, cytokines and immune complexes or during the phagocytic process. Release of low levels increases expression of cytokines and endothelial adhesion molecules, enhancing the inflammatory process. At high levels, they cause significant damage to endothelium leading to increased permeability.

Define natural barriers.

Our first line of defence includes the epithelial layer of the skin and mucous membranes lining the GI, genitourinary and respiratory tracts. These are "physical" barriers which can include mechanical and chemical types.

What is inflammation?

Our second line of defence. It is the protective response designed to eliminate the initial cause of injury, remove damaged tissue and generate new tissue. Similar definition: "the biochemical and cellular response of vascularized tissue to injury; designed to protect body from further injury".

Histamine

Present in preformed cells and is one of the first mediators to be released during acute inflammation. It is found in many places, including well-perfused connective tissue, where it is most prevalent, circulating platelets and basophils and within mast cell granules where it is released in response to trauma and immune reactions involving IgE. Histamine binds to H1 receptors on endothelial cells causing vasodilation, which helps increase blood flow to the microcirculation. It also contributes to vascular permeability by causing retraction of endothelial cells in capillaries and stimulates increased adherence of leukocytes to the endothelium. Also has neg consequence of contraction of smooth muscle of the bronchioles, making breathing difficult. Thankfully antihistamine (H1 receptor antagonist) medications are capable of binding to the H1 receptor to compete.

Cytokines and chemokines

Proteins that play a role in both acute and chronic inflammation and immunity. They are either pro-inflam or anti-inflam. They are produced by many cell types including activated macrophages and lymphocytes, endothelium, epithelium and connective tissue and modulate the inflammatory response by many other cells by travelling and binding to and affecting the function of those target cells.

Describe neutrophils.

Represent one type of granulocyte and are considered the chief phagocytic leukocytes. Early in the inflammatory response (90 mins to 6-12 hrs post injury) they are attracted to site by chemotactic factors. On their surface are found a number of different receptors each designed to recognize and interact with certain substances such a bacterial glycoproteins, microbes, cytokines, chemokines. Because of their lysosomal enzymes, they are called upon to destroy invaders and remove subsequent debris. Once they themselves die off they become exudate (pus). In presence of inflammation they are released form bone marrow and the neutrophil count will rise. They are relatively short lived because they are incapable of division and when they die off they release macrophage chemotactic factor to attract macrophages. In presence of severe inflammation, as demand for neutrophils increases the bone marrow can't keep up and release immature neutrophils called "bands". When the band count is elevated that means bone marrow is over worked.

Describe the cellular phase of inflammation.

Several simultaneous events occur during the vascular and cellular phases of inflammation. Wide gaps between cells of endothelial lining, allowing larger molecules and fluid to leak out into tissues. During normal condition, cells float within blood vessel continuously and the endothelium secretes nitric oxide, causing vasodilation, which limits sticking of cells to itself. During inflammation, as biochemical mediators are released from mast cells, activation of plasma proteins are released from dying cells and cause production of adhesion molecules on the surface of many cells involved in inflammation. These adhesion molecules cause certain cells (leukocytes and platelets) to become sticky and they adhere to endothelial wall.

Leukotrienes

Similar function to histamine and are synthesized while histamine is busy at work. They increase vascular permeability, induce smooth muscle contraction and constrict pulmonary airways, thus playing major role in mediation of asthma and anaphylaxis. In addition, they affect the adhesion properties of endothelial cells and the extravasation of chemotaxis of neutrophils, eosinophils, and monocytes. Because of their "late start" they help prolong the inflammatory response.

Serotonin

Similar to histamine in that it is released mainly by mast cells, basophils and platelets and causes smooth muscle contracting, small blood vessel dilation and increased vascular permeability.

Lysosomal enzymes

Small membrane enclosed sacs that contain very powerful enzymes. These lysosomes are capable of fusing with phagocytes for purpose of destroying foreign invaders.

Prostaglandins

Synthesized from arachidonic and metabolites and serve to induce inflammation and enhance effects of histamine and other mediators. Promote vasodilation and bronchoconstriction and increase neutrophil chemotaxis, cause pain through direct action on nerves and fever. The use of ASA and NSAIDs counteract this effect by inhibiting prostaglandin synthesis.

Describe the kinin system.

The 3rd plasma protein system and interacts closely with the clotting system. Both the clotting system and kinin system are initiated by activating factor XII. In this cascade, vasoactive peptides are generated from plasma proteins called kininogens by the action of proteases called kallekreins. Kallekreins can be found in tissue, and body fluids like saliva, sweat, urine, tears, feces, etc. The end result is production of BRADYKININ which causes vasodilation, increases vascular permeability, causes smooth muscle contraction, enhances leukocyte chemotaxis and stimulates pain receptors. Effects of bradykinin are similar to histamine, although effects much shorter as kinins are eventually degraded by kininases to maintain homeostasis. Bradykinin appears to be of greater importance during the latter phases of inflammation. Note: the presence of hageman factor (factor XII) is the initiator of kinin system. Hageman factor activates the following four components of the plasma protein systems: clotting cascade through factor XI, fibrinolytic system through conversion of plasminogen, kinin system by prekallekrein activator, and C1 and the complement cascade.

Describe the clotting system.

The clotting system is activated by substances released during tissue destruction and infection. There are 2 pathways (intrinsic and extrinsic) that converge at the place where factor X becomes Xa. Factor Xa and thrombin both act to provide the link between the coagulation system and inflammation. Inflammation is enhanced by many of the byproducts or fragments that are produced during the clotting cascade. Ex. during fibrin production, fibrinogen releases fibrinopeptides that are chemotactic for neutrophils, cause increase vascular permeability and enhance the effect of bradykinin from the kinin cascade. Similarly plasmin works with the complement cascade to activate C3a and C5a causing release of histamine. Factor XII is also called prekallekrein activator, an enzyme that activates prekallekrein in the kinase cascade. Primary goal of clotting system is to produce fibrous clot. The fibrinous network that forms serves to prevent the spread of infection by trapping the offending agent and retaining it at the site, to prevent bleeding and to provide framework for healing and repair.

What are adhesion molecules?

There are lots of biochemical mediators released from mast cells, plasma proteins and dying cells, which trigger the production of adhesion molecules on the surface of many cells. Adhesion molecules cause these cells to stick to or adhere to the endothelium.

Describe basophils.

Very similar function to eosinophils. They produce lipid mediators and cytokines to induce the inflammatory response. They are also important in allergic and hypersensitivity reactions. They also interact with immune system in that they bing to IgE through receptors on their cell surface which triggers release of histamine and vasoactive agents.

• Some offending microbes are tagged or opsonized by a complement factor known as C3b and by various antibodies of the immune system. Opsonization enhances recognition and binding activity of the phagocytes, acting like glue between the phagocyte and the target • Major phagocytes include monocytes, neutrophils and tissue macrophages are activated by injured tissue which triggers the leukocyte response for phagocytosis and cell killing. Neutrophils are then activated to form pseudopods that will encircle the offending organism or debris. Then, the phagocyte will fuse with an intracellular lysosome to form a phagolysosome which will released its enzymes and oxygen radicals to attack and destroy the offending microbe.

WOO HOO more memorizing...

• With any injury to tissue, there is an initial brief period of arteriolar vasoconstriction, followed by more profound vasodilation of the vessel. With vasodilation, the increased vessel size encourages increased volume of blood to the area of injury, and velocity of blood flow slows, increasing hydrostatic pressure. Biochemical mediators cause retraction of the endothelial cells, (increasing spaces between each cell) resulting in increased vascular permeability. As large proteins now leave the vessel and move into the extravascular space, they take fluid along with them. Blood then becomes more vicious, further slowing velocity of flow and leukocytes begin to stick to the endothelium and then migrate out of the site of injury. • Three major changes in microcirculation during vascular response of inflammation: 1: brief constriction, followed by vasodilation 2: increased capillary permeability 3. Movement of leukocytes into the tissue • This process leads to 5 cardinal signs of inflammation: heat, redness, edema, pain and loss of function.

YEPPP

• As learned earlier, as blood volume near the area of injury increases, hydrostatic pressure also increases and velocity of blood flow slows. Leukocytes in the area tend to linger here for a bit • A release of cytokines (those communication signals) cause the endothelium to express adhesion molecules that bind to leukocytes, tethering them to the endothelial wall, further leading to slugging forward movement of these cells. As leukocytes slow down, they adhere to the endothelial surface via intercellular adhesion molecules or ICAMs. Once attached to the ICAMs, the endothelial cells begin to separate and leukocytes work their way, via pseudopod-like movements, through these junctions. This process is called "transmigration" and is encouraged by a process called 'chemotaxis"

goodie...

Steps involving in phagocytosis. • Margination: leukocytes slow migration, adhere tightly to the endothelium, and move along the periphery of the blood vessels where they accumulate • Pseudopod formation: a process in which the plasma membrane of the phagocyte extends in finger-like projections • Diapedesis: movement of leukocytes through the widening junction between endothelial cells into the tissue • Migration: phagocytes move through the target • Opsonization: a process whereby adherence is enhanced between the phagocyte and the target cell • Engulfment: a process in which the phagocyte pseudopods surround and encircle the target, forming an intracellular phagocytic vacuole, or phagosome • Fusion with lysosome: a process whereby the phagosome merges with a lysosome to form a phagolysosome • Destruction: the target is destroyed; the ultimate goal of phagocytosis. Once phagocytes have destroyed the foreign material, they themselves die off and become exudate (pus). Phagocytic products exist via the lymphatics

when does it end...