Inflammation PDF

itis inflamation Inflammation itis: Suffix meaning inflammation. For example, colitis is literally colon inflammation or figuratively inflammation of the colon. The ending itis is one of the building blocks derived from Greek (in this case) or Latin used to construct medical terms meaning inflammati...

itis inflamation Inflammation itis: Suffix meaning inflammation. For example, colitis is literally colon inflammation or figuratively inflammation of the colon. The ending itis is one of the building blocks derived from Greek (in this case) or Latin used to construct medical terms meaning inflammation. Clinical correlation Acute bovine mastitis (photograph courtesy of Dr. Gordon Atkins, University of Calgary) - severe mastitis of the right hindquarter caused by Staphylococcus aureus. Bovine Acute Mastitis Mastitis is inflammation of the mammary gland Caused by the infection of glands with contagious or environmental bacteria Canbemetabolicissues Clinical or subclinical mastitis results in lower milk production, poor milk quality and adversely impacts the welfare of affected animals Causes large consumption oflukeocytes notforhuman A hallmark diagnostic feature of acute mastitis is the presence of leukocytes in the milk. Leukocytes, and other somatic cells, can be detected using a pen-side test called the California Mastitis Test (CMT).verypainfulmilkcollection This test uses the agglutination of DNA, which forms a gel in the milk, as an indicator of the presence of leukocytes Infectedmilkwillbe many viscous Automated cell counting can also assess the presence of cells in milk California Mastitis Test (CMT) Challenge question Describe the sequence of events that lead to acute mastitis Inflammation Dr Felix N. Toka Professor, Veterinary Immunology & Virology Department of Biomedical Sciences Objectives of this topic Understand what inflammation is and why it occurs Describe the signs of acute inflammation and their underlying mechanisms Describe the main mediators of acute inflammation Describe the vascular changes during acute inflammation Understand the role of leukocyte extravasation and the molecules involved Understand the manifestation of systemic inflammation Describe the resolution and outcomes of acute inflammation When the mechanical barrier of the innate immunity is breached (skin, mucous membranes) tissue injury induces a complex cascade of events that constitute I N F L A M M A T I O N Definition of inflammation: Tis ad Defense reaction of living tissue against damage, aimed at removing the cause of injury and repairing the tissue Inflammation plays an integral role in both innate and adaptive immunity Types of inflammation Inflammation may be acute or chronic Acute inflammation fights the early stages of infection and prepares the process that leads to tissue repair Chronic inflammation is characterized by the dominating presence of macrophages in the injured tissue Chronic inflammation functioningtissue Healthytissueisreplacedbydamagednon General causes of inflammation Exogenous causes: Physical agents Mechanical agents: fractures, foreign objects, sand, etc. Thermal agents: burns, freezing Chemical agents: toxic gases, acids, bases Biological agents: bacteria, viruses, parasites, fungi Endogenous causes: Fromwithin Circulation disorders: thrombosis, infarction, hemorrhage Metabolic products - e.g., uric acid, urea The hallmark (signs) of acute inflammation Fightsearlystagesofinfection Described by the Romans 2000 years ago: calor (heat) rubor (redness) tumor (swelling) dolor (pain) functio laesa (loss of function, added by Galen in the second century AD) How do signs of inflammation develop? Shortly after injury, vasodilation occurs leading to rise in blood flow to the area of injury rising the temperature (heat) Large volume of blood in the area of injury causes hyperaemia (redness) of the area of injury Vascular permeability increases leading to leakage of fluids from the blood vessels into the area of injury Fluid accumulation in injured tissue leads to oedema (swelling) How do signs of inflammation develop? Cont’d Within a few hours leukocytes adhere to the endothelium in the injured area leading to extravasation (passing of cells from blood into tissue) The leukocytes phagocytose invading pathogens and release mediators that further contribute to inflammation Some of these mediators are responsible for inducing pain in the area of injury Injured tissue is usually eliminated from normal function Mediators of Inflammation us 1. Pro-inflammatory cytokines (TNFα, IL-1, IL-6, IL-8) Tumor necrosis factor alpha (TNFα) and Interleukin 1 (IL-1) induce fever and stress hormone production (norepinephrine, vasopressin, activation of the renin-angiotensin-aldosterone system) TNFα and IL-1 induce synthesis of IL-6, IL-8 and interferon gamma (IFNγ) IL-6 stimulates the release of acute-phase proteins such as C-reactive protein (CRP) compound Initiatesclassical pathway Proinflammatory cytokines activate the coagulation cascade, release of nitric oxide, platelet-activating factor, prostaglandins, and leukotrienes Alltheseunderlinedthingsfurthermediateinflammation IL-1, IL-6 and IL-8 promote chemotaxis, induce extravasation of granulocytes and degranulation of neutrophils 2. Complement components C3a and C5a increase vascular permeability This playsarole intheinflammatoryprocess stimulate chemotaxis of neutrophils, eosinophils and monocytes Differentiate tomacrophages High factor indicates chemotactic whereneutrophilwill go Leukocyte Chemotaxis (photograph courtesy of Dr. Paul Kubes, University of Calgary) PGE PGEZ Az Thromboxane 3. Prostaglandins - (lipid soluble molecules derived from arachidonic acid) contribute to vasodilation, capillary permeability, pain and fever during inflammation to IRAs lower the blood pressure effect power Increase stable prostaglandins (PGE1 and PGE2) potentiate the effects of histamine and other inflammatory mediators Prostaglandin thromboxane A2 promotes platelet aggregation and vasoconstriction 4. Leukotrienes - (eicosanoid inflammatory mediators produced in leukocytes by the oxidation of arachidonic acid) - LTB4, LTC4, LTD4, LTE4 LTC4, LTD4 and LTE4 are referred to as slow-reacting substances of anaphylaxis (SRS-A) - they induce smooth muscle contraction LTB4 is a potent chemoattractant of neutrophils 19 a when 5. Vasoactive amines (histamine, serotonin) found at high concentration in platelets, basophils, and mast cells cause dilation and increased permeability of capillaries they act through H1 (histamine) and 5-HT (serotonin) receptors 6. Platelet-activating factor (PAF) generated from a lipid complex stored in cell membranes; affects a variety of cell types and induces platelet aggregation; It activates neutrophils and is a potent eosinophil chemoattractant; It contributes to exflux of plasma proteins leading to edema 7. Plasma Proteases Kinins – particularly bradykinin - increase capillary permeability causes (a role in hyperthermia and redness) andBrad pain my Clotting factors - production of fibrin peptides during the final steps of the clotting process Stages of Inflammation There are 2 important stages of inflammation, vascular and cellular stages (responses) triggered by entry of a pathogen in healthy tissues of the body The Vascular Stage (Response) ofthebloodvesselsfoundlocally immediatry Changes In time lmin Phase I - vasoconstriction - momentary constriction of small blood vessels in the area, begins 30 sec. after injury and lasts a few minutes Phase II - active vasodilation: Dilation of arterioles and capillaries (redness = rubor) Increase in blood flow more toyour Active hyperemia in inflamed region and increased cellular metabolism leading to higher local temperature (heat = calor) Phase III - passive vasodilation Blood vessels stop reacting to nervous and humoral stimuli Increase in vascular permeability causes swelling (tumor), pain, and impaired function Cellular stage (Response) tissue from bloodto Involves moving cens of Marked by movement of leukocytes into the area of injury Mainly granulocytes and monocytes to vessels tissues blood from moving The sequence of events includes: in Chemotaxis - leukocytes migrate in response to a chemical signal vessels begins blood Leukocytes Rolling - leukocytes slow down and increase their expression of adhesion molecules Migration - migrate into the tissue spaces nitwit Phagocytosis - neutrophils and macrophages engulf and degrade macrophages the bacteria and cellular debris https://www.youtube.com/watch?v=suCKm97yvyk Leukocyte trafficking When infection occurs, the immune system reacts immediately The first cells to arrive at the site of infection are cells of the innate immunity (granulocytes, (neutrophils), Mφ, NK) macrophages In order to arrive at the site, these cells need to move out of the vasculature Migration of leukocytes to sites of infection is highly regulated Foundon endothelium Cells of a given tissue are held together by cell adhesion molecules (CAM) However, cells of immune system are continuously in circulation In order for the cells of the immune system to participate in the inflammatory response, they need to use CAM to migrate to tissues where inflammation is taking place. into oftrna Extravasation of leukocytes from blood vessels into inflamed tissues or entrance of leukocytes into lymph nodes requires adhesion to the endothelium leakage veins from tissues surrounding Therefore, both the endothelium and leukocytes express CAM alwaysthere Most CAM are constitutively expressed and some CAM are expressed depending on local conditions present during inflammation (e.g., increase in cytokine or chemokine concentration) Some of the CAM present on leukocytes are required for leukocyteleukocyte interaction Therapeutic possibilities (formation of artheromas) Stop1123 Types of CAM 4 families of proteins Selectins Interact Mucins J Integrins Interact Ig-superfamily CAM Selectins notthesameasMBL Membrane glycoproteins containing extracellular lectin domains bind carbohydrate moieties found on mucin-like molecules The most important selectins are selectin E, L and P (CD62E, CD62L and CD62P, respectively) of surface Selectin L is expressed on leukocytes ofbloodcells Selectin P and E are expressed on the endothelium during inflammation Selectin P is contained in granules found in endothelial cells Selectin P is released when the granules fuse with the cell membrane Selectin E is synthesized de novo following stimulation by e.g., cytokines Selectins are responsible for leukocyte interaction with the endothelium during the initial vascular phase of inflammation FEasoconstrictin Mucins Bindtoselecting A group of heavily glycosylated, serineand threonine-rich proteins that bind to selectins Examples: CD34 or GlyCAM-1 on endothelial cells binds to CD62L on leukocytes, PSGL-1 on neutrophils binds to selectin E and P on endothelial cells Integrins Heterodimeric proteins consisting of α and β chains that are covalently joined at the cell surface 1 If The α and β chains form a binding site to which the Ig superfamily domains bindftp.iingd.tt Integrins are divided into subgroups according to type of β chain expressed (from β1 to β7) Leukocytes express integrins with β2 chain (CD18) Deficiency in β2 integrin leads to immunodeficiency called leukocyte adhesion deficiency (LAD) – an autosomal recessive disease manifested by recurrent bacterial infections In LAD neutrophils are unable to extravasate g RLeaknuacantleavebloodvess.is LAIfoundindogsaaoicows.ae Immunoglobulin CAM of the Ig-superfamily The name derives from the immunoglobulin-like domains they contain Additionally, they contain fibronectin domains Important representatives of Igsuperfamily CAMs are: ICAM-1 (CD154), ICAM-2 (CD102), ICAM-3 (CD50) and VCAM (CD106) Ig-superfamily CAMs bind to integrins They are expressed on endothelial cellscanalsobeonleukocytes Other CAMs may have structures that combine features of Ig-superfamily and mucins, e.g., MAdCAM-1 contain Ig-like domains and mucin domains Binatoselections Such CAMs (MAdCAM-1) are able to bind both selectins and integrins MAdCAM-1 is responsible for migration of leukocytes to the mucosa (e.g., it binds α4β7 (L-PAM) through its Ig-like domain and CD62L through its mucin domain) a Leukocyte extravasation Leakageleaving thevessels During the initiation of inflammation, cytokines and other mediators of inflammation stimulate the endothelial cells, leading to increased expression of CAMs This process is referred to as endothelial cell activation Leukocytes can now exit the blood vessels into the inflamed tissue Extravasation of leukocytes is divided into 4 phases Leavingthevessels l oosely mucinselectinsbind toanowroning Phase I L CAMs, Rolling – At the site of injury, leukocytes, with the aid of their mucin c loosely bind to selectin E and P on the endothelial cells. Their movement slows down and they begin to roll on the endothelium Increaseinexpression m olecules adhesion of Phase II Activation Increase in cytokine, particularly chemokine secretion by endothelial cells Increase in chemokine receptor expression on leukocytes leading to activation of leukocytes shapechangingallows to integrins onleukocytes sunan tight u sing bind Phase III stops m oving Cell Adhesion (strict adhesion) Activation of the endothelium and leukocytes produces conformational changes in cells Integrins on leukocytes can now bind firmly to the endothelium Phase IV Diapedesis (transendothelial migration) Leukocyte squeeze in between two neighbouring endothelial cells and pass into the inflamed tissue Leukocytes use homotypic binding of platelet-endothelial-cell adhesion molecule 1 (PECAM-1 (CD131)) on the endothelium (self-to-self binding) Neutrophil extravasation Leakageleaving thevessels Neutrophils are among the first cells to arrive at the site of inflammation Neutrophils do not bind to endothelial cells under normal circumstances (i.e., without inflammation) Without inflammation there is no expression of selectin E, P and other CAMs on the endothelium – expression has to be induced is forselectinE Pexpression Inflamation needed endothelial cens m ucin bind camto use toserineandPon leukocytes pson useselection mucin Neutrophils Selectin L and mucin PSGL-1 are responsible for rolling of neutrophils IL-8 and MIP-1β are responsible for activation of neutrophils during extravasation Activation also leads to increased expression of ICAM on the endothelium and CD11a/CD18, CD11b/CD18 (LFA-1 and MAC-1) on neutrophils, leading to firm adhesion and finally diapedesis It p The chemokine gradient then leads the neutrophils to the focal point of inflammation Extravasation of monocytes out Allotthese.don.tman.it circulation firsttoarriveatthesite the NoteLeukocytesare Monocytes arrive slightly late at the site of inflammation, because high expression of VCAM-1 and ICAM-1 is possible only after the activation stage Only a small subset of monocytes can extravasate under normal circumstances for the purpose of replenishing tissue macrophages and dendritic cells This homeostatic migration is constitutively regulated by CXCL14 Monocyte migration cont’d CD62L are responsible for rolling MCP-1 regulates activation PECAM-1 responsible for diapedesis Complement receptors such as CR3 and CR4, bacterial peptides participate in extravasation of monocytes into inflamed tissue Migration of lymphocytes Lymphocytes are continuously circulating between blood and lymphatic tissues Migration of lymphocytes Extravasation of lymphocytes is similar to that of neutrophils Samemechanism Lymphocytes will migrate to areas where there is an infection Lymphocytes use the same mechanism to extravasate into inflammatory sites or secondary lymphoid organs They pass through post capillary venules called high endothelial venules (HEV) I Scanning microscope view of HEV Selectins E and P, mucins, GlyCAM-1 and CD34, and CAMs from the Igsuperfamily (ICAM-1, ICAM-2, ICAM-3, VCAM-1 and MAdCAM-1) are involved n iÉ Activation of lymphocytes in HEVs prior to extravasation is mediated by igIs Involved chemokines CCL19, CCL21 and CXCL12 Thispartisspecifictolymphocytes Inflammation RolecleanRepair tissue thesiteof dam Cells and mediators involved in a local acute inflammatory response I t.Y.in Systemic manifestations of inflammation Under optimal conditions, the inflammatory response remains confined to a localized area. In some cases local injury can result in prominent systemic manifestations as inflammatory mediators are released into the circulation. The most prominent systemic manifestations of inflammation are: The acute phase response Low High Alterations in white blood cell count (leukocytosis or leukopenia) High fever Sepsis and septic shock, also called the systemic inflammatory response Organs and mediators involved in Systemic AcutePhase Response common creactiveprotein Most of Amount proinflammatorycytokines initiatesinflammatoryresponse Acute phase response Takesplaceinserumduringbacterial infections Changes in serum proteins during infection isAPR referred to as acute phase response (APR) Proteins whose concentrations increase or decrease during infection I I 1 1 are referred to as acute phase response proteins (APP) 5Th APRisserumproteins Important examples: some complement system proteins, C-reactive proteins (CRP) are part of the innate immune response Acute phase response proteins are induced by signals that travel through blood from the site of injury or infection Synthesis is induced by pro-inflammatory cytokines produced by phagocytes (TNFα, IL-1, IL-6) Most APR proteins are synthesized in the liver Acute Phase Proteins C-reactive proteins (CRP) belong to Pentraxins (pentameric proteins) Ligands for CRP are pneumococcal polysaccharides and phosphorylcholine CRP bound to the surface of a microbe promotes uptake by phagocytes and activates complement-mediated attack Mannose-binding lectin is an acute phase response protein that recognizes mannose on microbes and not vertebrate cells Other systemic effects of inflammation loss of appetite (anorexia) altered sleep patterns lethargy muscular wasting (cachexia) metabolic acidosis (lowered blood pH) Resolution of inflammation When no longer required, inflammatory response must be actively terminated to prevent unnecessary damage to tissues. Failure to do so results in chronic inflammation and cellular destruction. Resolution of inflammation occurs by different mechanisms in different tissues. Inflammation termination mechanisms include: Short half-life of inflammatory mediators in vivo Production and release of transforming growth factor (TGF) beta from macrophages IL-4 and IL-10 induce downregulation of TNFa, IL-1, IL-6, and IL-8 stop 123 Inflammation termination cont’d Downregulation of pro-inflammatory molecules, such as leukotrienes Upregulation of anti-inflammatory molecules such as the Interleukin 1 receptor antagonist or the soluble tumor necrosis factor receptor; Apoptosis of pro-inflammatory cells Downregulation of receptor activity by high concentrations of ligands Production of anti-inflammatory lipoxins At end stages of inflammation, granulocytes promote arachidonic acid–derived lipoxins, which initiate the termination sequence Neutrophil recruitment thus ceases and programmed death by apoptosis is engaged Additionally, resolvins and protectins synthesized from omega-3 polyunsaturated fatty acids shorten the period of neutrophil infiltration by initiating apoptosis The anti-inflammatory program ends with the departure of macrophages through the lymphatics Outcomes of inflammation Resolution Complete restoration of the inflamed tissue, parenchymal cell regeneration - short lived inflammation Fibrosis Extensive tissue destruction – formation of a scar composed largely of collagen - functional impairment may occur Abscess formation A cavity containing pus is formed Chronic inflammation Persistence of injurious agent - prolonged inflammation with dominating presence of macrophages in the injured tissue - tissue destruction