Inflammation I, Wound Healing & Repair. Acute.pptx

ACUTE Inflammation Dr. Maxy A. C. Odike MBBS, MSc, FMCPath, FICS, FCPath (ECSA), Dip (Res Ethics) Professor of Pathology Ambrose Alli University, Ekpoma October, 2018 Have you had an injury before? What caused the injury? What did you feel? What did you see at site of injury? Did the injury eventual...

ACUTE Inflammation Dr. Maxy A. C. Odike MBBS, MSc, FMCPath, FICS, FCPath (ECSA), Dip (Res Ethics) Professor of Pathology Ambrose Alli University, Ekpoma October, 2018 Have you had an injury before? What caused the injury? What did you feel? What did you see at site of injury? Did the injury eventually heal? Introduction         Response of vascularized living tissues to injury Serves to deliver cells and molecules of host defence from the circulation to the sites of injury, in order to eliminate the offence. Not a disease; very vital for wound healing Therefore, basically a protective process, but May bring discomfort/harm: ranging from local tissue damage, to serious disease (e.g., auto-immune diseases, hypersensitivity reactions, allergies), common chronic diseases (e.g., rheumatoid arthritis, atherosclerosis, and lung fibrosis), and others (e.g., type 2 DM, Alzheimer disease, and cancer: cirrhosis > carcinoma) The processes (Vascular and Cellular events) are mediated by sets of chemicals – The Chemical Mediators of Inflammation Inflammatory conditions are usually described by the suffix '-itis‘ Classified into Acute or Chronic; and can occur in any organ Major Cellular & Tissue Participants in Inflammation Circulating cells: neutrophils, monocytes, eosinophils, lymphocytes, basophils, and platelets. Connective tissue cells: mast cells (which intimately surround blood vessels); fibroblasts; resident macrophages; and lymphocytes Extracellular matrix: Structural fibrous proteins (collagen, elastin); adhesive glycoproteins (fibronectin, laminin, nonfibrillar collagen, tenascin, and others); and proteoglycans. Basement membrane is a part of ECM, consisting of adhesive glycoproteins and proteoglycans. Classification   Acute: initial rapid response characterized by vascular changes, exudative edema and neutrophilic infiltration Chronic : protracted response characterised by infiltration of mononuclear cells i.e. macrophages, lymphocytes and plasma cells, along with tissue destruction and repair by fibrosis Historical highlights The study of inflammation has a rich history:  ~ 3000 BC - clinical features of inflammation described in an Egyptian papyrus  First Century AD - Cornelius Celsus, first listed 4 Cardinal Signs or Hallmarks of inflammation (Celsus tetrad of inflammation): rubor (redness), tumor (swelling), calor (heat), and dolor (pain)  19th Century AD - a 5th clinical sign, functio laesa (loss of function) was added by Rudolf Virchow  1793, Scottish surgeon John Hunter noted: inflammation is not a disease but a stereotypic response that has a salutary effect on its own  1880s - Russian biologist Elie Metchnikoff discovered phagocytosis, and concluded that the purpose of inflammation was to bring phagocytic cells to the injured area to engulf invading bacteria Signs of Acute Inflammation Aulus Cornelius Celsus (25 BC – 50 AD) 1st Century AD: 4 Cardinal Signs or Hallmarks of inflammation, aka Celsus Tetrad of Inflammation Rudolf Virchow (1821-1902) 19th Century AD: 5th clinical sign, functio laesa (loss of function) John Hunter (1728–1793) 18th Century AD: Inflammation- not a disease but a stereotypic response that has a salutary effect on its Julius Cohnheim (1839–1884)  First used the microscope to observe inflamed blood vessels in thin, transparent membranes (mesentery and tongue of the frog)  Noted the initial changes in blood flow, the subsequent edema caused by increased vascular permeability, and the characteristic leukocyte emigration 1910) Characterized the pus cells in acute inflammation, and showed that pus cells could migrate from the places of their origin in the interstitium to other tissues and epithelial cells Thomas Lewis Described the importance of chemical mediators in 1927 Benefits of Inflammation  Inactivates injurious agent(s)  Breaks down and removes dead tissue(s)  Initiates healing of tissue injury(ies)  Transport and delivery of drugs, such as antibiotics, to sites of injury(ies)  Fibrin formed from exuded fibrinogen impede the movement of microorganisms, trap them, and so facilitate phagocytosis Causes of inflammation Inflammation may be triggered by a variety of stimuli:      Infections (bacterial, viral, fungal, parasitic) and microbial toxins are among the most common and medically important causes. Tissue injury/necrosis, which may include ischemia, physical and chemical injury. Injured/necrotic cells release some molecules that trigger inflammation. Foreign bodies (splinters, dirt, sutures) may elicit inflammation by themselves or because they cause traumatic tissue injury or carry microbes. Immune reactions, which include hypersensitivity reactions, autoimmune diseases, or allergies Combined cause is seen in many cases ACUTE INFLAMMATION Acute inflammation process has three major components:  (1) dilation of small vessels leading to an increase in blood flow, i.e., change in vascular flow and caliber  (2) increased permeability of the microvasculature enabling plasma proteins and leukocytes (exudate) to leave the circulation, and  (3) emigration of the leukocytes from the microcirculation, their accumulation in the focus of injury, and their activation to eliminate the offending agent.  The first 2 make up the Vascular events, while the third makes up the Cellular events of inflammation. Vascular events in acute inflammation Changes in Vascular Flow and Caliber Vasodilation of arterioles >> increased blood flow to area [hence the heat and redness (erythema)] Increased permeability of microvasculature >> exudation into the extravascular tissues [hence the swelling] Slowing of blood flow, concentration of red cells in small vessels [i.e, congestion (stasis)] WBCs, principally neutrophils, resting along the endothelium. Endothelial cells are activated, and express adhesion molecules. Increased Vascular Permeability May be achieved by: Contraction of endothelial cells – produces the immediate transient response [rapid and short-lived (15 to 30 minutes)]. Chemical mediated. Endothelial injury, necrosis and detachment. Seen in severe injuries (e.g., burns, uv radiation), microbial infections, infiltrating neutrophils. May produce immediate or delayed (few hours sunburn) leakage, which lasts for several hours Increased transport of fluids and proteins, called transcytosis, through the endothelial cell. Although these mechanisms are Change in vascular flow & caliber, and increased permeability Vascular leakage in Inflammatory Edema – The Exudate Vascular leakage in Noninflammatory Edema – The Transudate Normally, hydrostatic and osmotic forces are nearly balanced so that there is little net movement of fluid out of vessels. Many pathologic disorders (Table) cause increases in capillary hydrostatic pressure or decreases in plasma osmotic pressure that lead to the extravasation of fluid into tissues. Lymphatic vessels remove much of Transudate vs Exudate low protein content (mostly albumin); SG less than 1.012; essentially an ultrafiltrate inflammatory; high protein concentration, cellular debris; SG above 1.020; increased Methods for Increased Vascular Permeability Tissue oedema Neutrophil margination …. And emigration Responses of Lymphatics and Lymph Nodes in inflammation   Lymphatics proliferate like blood vessels during inflammation to handle the increased load Lymph flow is increased and helps drain the edema fluid from the extravascular space  Lymphatics and lymph nodes filter and police the extravascular fluids, and may drain leukocytes and cell debris, as well as microbes, into lymph when severe  Such lymphatics may then become secondarily inflamed (lymphangitis), as may the draining lymph nodes (lymphadenitis), which may become enlarged because of hyperplasia of the lymphoid follicles and increased numbers of lymphocytes and macrophages (referred to as reactive, or inflammatory, lymphadenitis) Cellular events in acute inflammation  Series of cellular activities closely follow the vascular events in inflammation  Aim: quick delivery of leukocytes to the site of injury, necrosis or infection, for elimination of offending agents  Leukocytes also produce growth factors and other chemicals that aid in repair  Most important leukocytes in typical acute inflammation are the ones capable of phagocytosis: Neutrophils and Macrophages  Side effects may result: tissue damage and therefore, prolonged inflammation, Cellular activities  Composed of multi-step process delivery of leukocytes from the vessel lumen to the tissue, and phagocytosis  Mediated by adhesion molecules and cytokines: 1.In the lumen: margination, rolling, and adhesion to endothelium (pavementing) 2.Transmigration (Diapedesis) across the endothelium and vessel wall 3.Migration (Chemotaxis) in the tissues toward a chemotactic stimulus 4.Phagocytosis and clearance of offending agent Rolling: white cells adhering transiently to the endothelium, detach and bind again, as they flow along on the vessel wall Adhesion: white cells finally come to rest at some point where they adhere firmly, appearing like pebbles. Margination: white cells assuming more peripheral orientation along the endothelial surface  The attachment of WBCs to endothelial cells is mediated by adhesion molecules on the two cell types.  Their expression is enhanced by cytokines during inflammation.  Two major families and their ligands are involved in leukocyte adhesion Adhesion Molecules (PECAM-1) Multistep process of Neutrophil migration:  Neutrophil first roll, then become activated and adhere to endothelium, then transmigrate across the endothelium, pierce the basement membrane, and migrate toward chemoattractants emanating from the source of injury.  Different molecules involved: a. Selectins in rolling; b. Chemokines in activating the neutrophils to increase avidity of integrins; c. Integrins in firm adhesion; and d. CD31 (PECAM-1), CD106 (VCAM-1) and CD54 (ICAM -1) (members of Immunoglobulin super family) in transmigration. ICAM-1, Intercellular adhesion molecule 1; VCAM-1, vascular cell adhesion molecule 1; PECAM-1 (CD31), platelet endothelial cell adhesion molecule-1; TNF, tumor necrosis factor. Selectins Mediate the initial rolling interactions – a low affinity binding 3 types: L-­selectin (expressed on leukocytes ), E-­ selectin (on endothelium), and P-­selectin (in platelets and on endothelium) Ligands for selectins are sialylated oligosaccharides bound to mucin­-like glycoproteins TNF and IL-1 act on Ligand for by inflammation Their expression is upregulated E and P-selectins the endothelial cells cytokines (IL-1, TNF, histamine & thrombin) of post-capillary Ligand for L-selectin (GlyCam1) venules and induce the coordinate expression of numerous adhesion molecules (E­ selectin and the ligands for L-­ selectin) within 1 Weibel-Palade Bodies are intracellular stores in endothelial cell granules Integrins Is a family of heterodimeric leukocyte surface proteins Mediate firm adhesion of WBCs to endothelium (pavementing) 2 types: β1 integrin (VLA­4), and β2 integrins (LFA­ 1 and Mac­1) Their endothelial ligands, mainly vascular cell adhesion molecule 1 (VCAM­1- ligand for β1 integrin) and intercellular adhesion molecule­1 (ICAM­1- ligand for β2 integrins) are induced by TNF & IL-1. WBCs normally express integrins in a low affinity state. With activation by chemokines, VLA­4 and LFA­ 1 integrins on the rolling WBCs are converted to a (LFA1, MAC1, VLA4) VCAM-1 Why Neutrophils first…?  They are more numerous in the blood than other leukocytes,  They respond more rapidly to chemokines, and  They may attach more firmly to the adhesion molecules that are rapidly induced on endothelial cells, such as P- and E-selectins Filopodia Nature of leukocyte infiltrates in inflammatory reactions. The photomicrographs show an inflammatory reaction in the myocardium after ischemic necrosis (infarction). A, Early (neutrophilic) infiltrates and congested blood vessels. B, Later (mononuclear) cellular infiltrates. C, The approximate kinetics of edema and cellular infiltration. For simplicity, edema is shown as an acute transient response, although secondary waves Phagocytosis and Clearance of  Offending Recognition ofAgents microbes or dead cells induces several responses in leukocytes - leukocyte activation  Activation is through stimulation of signaling pathways in leukocytes that result in increases in cytosolic Ca2+, then activation of enzymesprotein kinase C and phospholipase A2.  Phagocytosis involves 3 sequential steps: o recognition and attachment of the particle to be ingested by the leukocyte o engulfment, with subsequent formation of a phagocytic vacuole o killing or degradation of the ingested material Recognition and Attachment 3 types of receptors are described: a. Mannose receptors: binds terminal mannose and fucose residues of glycoproteins and glycolipids, which are typically part of molecules found on microbial cell walls b. Scavenger receptors: macrophage integrins, especially Mac-1 (CD11b/CD18), bind a variety of microbes in addition to modified LDL (oxidized or acetylated) particles c. Receptors for various opsonins: phagocytosis is enhanced when microbes are attached to specific proteins called opsonins (opsonisation). Phagocytes express high affinity receptors for opsonins. Major opsonins: IgG antibodies, C3b   Engulfm ent Soon after attachment, extensions of cytoplasm (pseudopods) flow around the attached particle, and the plasma membrane pinches off to form an intra-cytoplasmic vesicle (phagosome) that encloses the particle. Phagosome then fuses with a lysosome, forming phagolysosome, into which the contents of the lysosome are discharged Intra-cellular killing or degradation Final step in elimination of agents and phagocytosed debris  Acccomplished by:  Reactive oxygen species [ROS – Hypochlorite (HOCl-), Hydroxyl radical (-OH)]  Reactive nitrogen species, [RNS – Peroxynitrite(ONOO-)]  Lysosomal enzymes (Acid hydrolases – proteases, elastases, defensins, lysozyme, lactoferrin, MBP, cathelicidins, permeability increasing protein, etc )  iNOS – inducible nitric oxide synthase  Oxygen-derived free radicals may be released extracellularly from leukocytes, and result in tissue damage accompanying inflammation  Serum, tissue fluids, and host cells possess antioxidant mechanisms that protect against these harmful radicals: (1) Superoxide dismutase, (2) Catalase (detoxifies H2O2) (3) Glutathione peroxidase, another powerful H2O2 detoxifier (4) the copper-containing serum protein ceruloplasmin, and (5) the iron-free fraction of serum transferrin.  Harmful effects of released lysosomal enzymes (proteases) are controlled by a system of anti-proteases Leukocyte-mediated Tissue Injury Leukocytes cause injury to normal cells and tissues in some circumstances: 1. As part of a normal defense reaction against infectious microbes, when adjacent tissues suffer collateral damage, due to leakage of contents of lysosomes (e.g., abscess, TB) 2. When the inflammatory response is inappropriately directed against host tissues. (e.g., certain autoimmune diseases) 3. When the host reacts excessively against usually harmless environmental substances, as in allergic diseases, including asthma Contents of WBC lysosomal granules can leak into the extracellular milieu by several mechanisms: a. Frustrated phagocytosis- follows attempts to phagocytose materials on immovable flat surfaces (e.g., glomerular basement membrane). b. Regurgitation during feeding- phagocytic vacuole remains transiently open to the outside before complete closure of the phagolysosome. So toxic Termination of the Acute Inflammatory Response Tight controls of inflammation, to minimize damage: 1. Inflammation generally declines after the offending agents are removed simply because the mediators of inflammation are produced in rapid bursts, only as long as the stimulus persists, have short halflives, and are degraded after their release 2. Neutrophils have short half-lives in tissues and die by apoptosis within a few hours after leaving the blood 3. As inflammation develops, the process itself triggers a variety of stop signals that actively terminate the reaction: switch in the type of arachidonic acid metabolite produced, from proinflammatory leukotrienes to anti-inflammatory lipoxins; and release of anti-inflammatory cytokines (e.g.,TGF-β and IL-10) from macrophages and other cells 4. Others- including neural impulses (cholinergic discharge) that References  KumarV, Abbas AK and Fausto, eds. Robbins and Cotran pathologic basis of disease. 9th ed. Philadelphia, WB Saunders Co, 2015; 1263 – 1264; chapter 3; Inflammation and Repair; pages 69 – 74  KumarV, Abbas AK and Fausto, eds. Robbins and Cotran pathologic basis of disease. 7th ed. Philadelphia, WB Saunders Co, 2005; ISBN 0-8089-2302-1chapter 2; Acute and Chronic Inflammation; pages 48 – 54  Prichard, R. (1961). Selected Items from the History of Pathology. Am J Pathol. 1979 November; 97(2): 314. [Online]. Available http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2042458/pdf/amjpathol00237-0113.pdf  John E. Hall, Arthur C. Guyton; Guyton and Hall Textbook of Medical Physiology. 12th ed. Philadelphia, PA 19103-2899; Saunders 2005; ISBN: 978-1-4160-4574-8; chapter 14; Overview of the Circulation; Biophysics of Pressure, Flow, and Resistance; pages 157 - 166  Heidland, A., Klassen, A., Sebekova K, Bahner U. (2009). Beginning of modern concept of inflammation: the work of Friedrich Daniel von Recklinghausen and Julius Friedrich Cohnheim. J Nephrol. 2009 NovDec; 22 Suppl 14:71-9. [Online]. Available http://www.ncbi.nlm.nih.gov/pubmed/20013736  Alitalo K: The lymphatic vasculature in disease. Nat Med 17:1371–80, 2011. [An excellent review of the cell biology of lymphatic vessels, their functions in immune and inflammatory reactions, and their roles in inflammatory, neoplastic and other diseases.]  Vestweber D: Relevance of endothelial junctions in leukocyte extravasation and vascular permeability. Ann N Y Acad Sci 1257:184–92, 2012. [A good review of the basic processes of vascular permeability and how interendothelial junctions are regulated.]  Takeuchi O, Akira S: Pattern recognition receptors and inflammation. Cell 140:805, 2010. [An excellent overview of Toll-like receptors and other pattern recognition receptor families, and their roles in host defense and inflammation.]  Hedwig S. Murphy; Overview Of Inflammation