Inflammation (Part 1 – Acute Inflammation) PDF

Inflammation (Part 1 – Acute Inflammation) Dr Gianluca Farrugia [email protected] 1 Learning Objectives 1. Define inflammation, symptoms and list its cardinal signs. 2. Describe the vascular & cellular processes that characterise the acute inflammatory response, more specifically the formation o...

Inflammation (Part 1 – Acute Inflammation) Dr Gianluca Farrugia [email protected] 1 Learning Objectives 1. Define inflammation, symptoms and list its cardinal signs. 2. Describe the vascular & cellular processes that characterise the acute inflammatory response, more specifically the formation of the inflammatory fluid exudate. 3. Define the term 'mediator of inflammation’ , list the prominent mediators of inflammation and their basic functions. 4. List the outcomes of acute inflammation. [Note – diagrams serve as learning aids & additional notes on some slides are not examinable.] 2 Definition: Inflammation is an immune response of living tissue to injury, caused by harmful stimuli or insults. The inflammation of bodily tissues can be inferred by addition of the suffix ‘itis’, as exemplified below: Hepatitis Endocarditis Cystitis, Dermatitis, Pneumonitis (pneumonia) - inflammation of liver tissue - inflammation of endocardial wall - inflammation of the bladder - inflammation of skin tissue - inflammation of lung tissue [“Infjammazzjoni” (In-fyam-atss-yo-ni) – Maltese term for “inflammation”.] 3 The main functions of inflammation are to: serve as an all-purpose defence mechanism of the innate immune system, contain and isolate cell and tissue injury, neutralise, destroy and clear away infectious micro-organisms, achieve repair and healing (where possible) of damaged tissues. ideally resolve (i.e. conclude itself and clear away immune cells to facilitate resumed normal tissue function) upon elimination of infection and/or completion of tissue repair. Hence, properly regulated inflammation is a finite process [acute inflammation]. 4 Acute Inflammation vs Chronic Inflammation - ACUTE Inflammation: - an immediate inflammatory response to injury. - a finite (temporary) inflammatory process that can last minutes, hours, days or maybe weeks until resolution. - failure of acute inflammation to resolve can result in chronic inflammation. - CHRONIC Inflammation: - a prolonged period of inflammation largely caused by uncontrolled acute inflammation that has failed to resolve itself. - can last months to years. - implicated in development of chronic diseases (e.g. diabetes) and cancer. 5 Signs and Symptoms of Acute Inflammation Systemic Symptoms of Acute Inflammation Pyrexia (fever), drowsiness, lethargy, decreased appetite à sickness behaviour Cardinal Signs of Acute Inflammation are the following macroscopic changes: Redness (rubor) Heat (calor) – (not the same as pyrexia) Pain (dolor) Swelling (tumor) Loss of function (functio laesa) 6 Cardinal signs of acute inflammation in injured tissues are caused by a sequence of cellular and/or vascular processes: Cardinal sign Vascular and/or cellular process Redness (Rubor) Increased blood flow Heat (Calor) Increased blood flow Exudation of fluid Release of inflammatory mediators Swelling (Tumor) Exudation of fluid & protein (exudate) from blood vessels into tissues. Pain (Dolor) Release of inflammatory mediators Exudate fluid stretching pain receptors & nerves Loss of function (Functio laesa) Disruption of tissue structure 7 Immune cells involved in acute inflammation Neutrophils (polymorphonuclear neutrophils -PMNs) circulating immune cells and first cell to arrive in inflamed tissue. predominant immune cell type for first 6-24h. segmented nucleus, granular cytoplasm full of granules containing enzymes etc. most abundant polymorph – mainly combat bacteria and fungal infections. first line of defence vs infection and potent effectors of inflammation. Monocytes circulating immune cells that migrate into tissue following signal from inflammatory mediators and in tissue mature into phagocytic macrophages. Macrophages derived from circulating monocytes in blood. predominate after 24h. attack pathogens and clear up debris via phagocytosis. 8 Immune cells involved in acute inflammation Eosinophils Respond especially to allergies and helminth infections. Bilobed nucleus and abundance of red granules in cytoplasm. Mast cells Tissue resident cell. Small nucleus, cytoplasm packed with blue granules. Releases granules containing vasoactive amines (histamine). Natural Killer Lymphocytes Circulating immune cells. Directly lyse virally infected cells, tumour cells or antibody-coated cells. Release pro-inflammatory cytokines. 9 Acute Inflammation Initiation in Four Steps Extrinsic Factors: Biological: infection (e.g. virus, bacteria, fungi) Chemical: acids, heavy metals, harmful fumes), Physical: cuts, extreme temperatures (burns & frostbite) Intrinsic Factors: Biological, chemical or physical: Anoxia (absence of oxygen) stomach acid à gastric ulcers metabolic products (e.g. urate crystals in joints à gouty arthritis) Necrosis Immunological (e.g. hypersensitivity reactions) 10 Acute Inflammation – Step 1 – tissue damage and mediator release 11 Inflammatory mediators Endogenous chemical agents that to act to promote inflammation NB. Cells include damaged cells and immune cells Inflammatory mediators & cytokines Acute Inflammation – Step 2 – fluid and cellular influx into tissue 14 Acute Inflammation – Step 2 – fluid influx into tissue Normal Plasma proteins in circulation Transudate Fluid leaks into tissue but proteins remain in circulation Exudate Fluid and proteins leak into tissue 15 Acute Inflammation – Step 2 – cellular influx into tissue Leukocytes in blood stream gather towards margins of blood vessels Leukocytes stick firmly to the endothelial vessel Leukocytes cross the endothelial wall Leukocytes move towards chemoattractants by CHEMOTAXIS 16 Acute Inflammation – Step 3 – cells move to site of inflammation 17 Chemotaxis Directional movement of cells towards an extracellular chemoattractant molecules, against a concentration gradient. Chemoattractants include: Bacterial & fungal products (i.e. N-formylmethionyl-leucyl-phenylalanine [fMLF or fMLP]) Pro-inflammatory mediators Leukotrienes and prostaglandins Chemokines (group of cytokines) Complement components C5a & C3a 18 Cellular influx into tissue and to site of inflammation 19 Acute Inflammation – Step 4 – cells and mediators kill bacteria 20 Acute Inflammation – Step 4 Phagocytosis - the recognition, engulfment and 1. Phagosome digestion of material by phagocytic cells (phagocytes) 1. Phagocytes engulf material by extension of pseudopods to form a phagosome. 2. 2. 3. Phagolysosome 4. Phagosome fuses with lysosomes containing oxygendependent degradative molecules (i.e. hydrolytic enzymes) to form a mature phagolysosome. 3. The engulfed material is destroyed 4. Remnants discarded phagolysosome contents may harm surrounding tissues 21 Opsonisation enhances phagocytosis * Macrophage * Opsonisation is the enhancement of phagocytosis by opsonin molecules (*) (antibody and/or complement molecules) which coat antigens and mark them for elimination by phagocytes (macrophages and neutrophils). 22 Acute Inflammation – Step 4 – cells and mediators kill bacteria Release of Neutrophil Extracellular Traps (NETs) by process of NETosis 23 Summary of acute inflammation: The cascade of inflammatory mediators in response to tissue injury. End result of this cascade: i) more leucocytes drawn to inflamed area via increased blood flow & chemotaxis, ii) enhanced adhesion of leucocytes to blood vessel walls due to sticky integrins, iii) better-facilitated entry of leucocytes into injured tissue via extravasation, due to leaky vessels and chemotaxis. iv) faster clearance of pathogens & damaged cell contents & resolution. 24 Outcomes of inflammation 25 Outcomes of inflammation: sepsis Pathogenic microorganism gains access to lymphatic system then circulatory systems, or the circulatory system directly. Medical emergency as mortality is high Sepsis is a continuum SIRS: Systemic inflammatory response syndrome 26 Investigating inflammation Blood tests ―Acute phase proteins ―blood C-reactive protein (CRP) ―blood erythrocyte sedimentation rate (ESR) ―Tests for immune cells ―Full blood count high white blood cell count, particularly neutrophils (neutrophilia) BUT in severe inflammation (sepsis) neutrophils can be reduced (neutropenia) Note: variations with age, sex, ethnicity etc. 27 Inflammation (Part 2 – Chronic Inflammation & Wound Healing) Dr Gianluca Farrugia [email protected] 28 Learning Objectives 1. Distinguish between acute and chronic inflammation. 2. List the outcomes of chronic inflammation. 3. Define the composition, formation and function of cellular infiltrate in chronic inflammation? 4. Know the basic features of granulomatous chronic inflammation. 5. Describe the four stages of wound healing, its outcomes and complications. [Note – diagrams serve as learning aids & additional notes on some slides are not examinable.] 29 Acute vs Chronic Inflammation Acute inflammation Chronic inflammation Causative agent Injured tissue Pathogens Persistent acute inflammation Persistent exposure to toxic agents Immune mediated (hypersensitivity) Major cells involved Neutrophils Monocytes Mast cells Macrophages Lymphocytes Plasma cells Fibroblasts Onset Immediate Delayed Duration Days Weeks - years Outcomes Healing Abscess formation Chronic inflammation Tissue destruction Fibrosis 30 Cells involved in Chronic inflammation B cells (lymphocytes) and B-cell-derived plasma cells Antigen specific receptors for recognition of antigen in 3D conformation. B cells mature into plasma cells which produce and secrete antibodies (immunoglobulins). Immunoglobulins (Ig) tag pathogens, marking them for destruction. Plasma cell T cells (lymphocytes) Antigen specific receptors for recognition of linear peptide. Cytotoxic T cells (e.g. CD8 T cells) activated if recognition of peptides derived from endogenous sources, typically virally infected or cancer cells, for direct killing. Helper T cells (e.g. CD4 T cells) activated if recognition of peptides derived from exogenous sources expressed on antigen presenting cells (APC), for cytokine production and release to activate other immune cells Lymphocytes 31 Cells involved in Chronic inflammation Fibroblasts Proliferate in response to chemokines secreted by macrophages. Synthesise extracellular matrix and collagen. Macrophages: Tissue residence cells that mature from monocytes. Activation via cytokines (IFN-γ) or through pattern recognition receptors (PRRs) by Damage associated molecular patterns (DAMPS) Pattern associated molecular patterns (PAMPS). Numerous functions digestion/ killing of bacteria digestion of extracellular matrix stimulation of angiogenesis (blood vessel formation in wound healing) recruitment of other inflammatory cells 32 Histological appearances of chronic inflammation Presence of: Mixed inflammatory cell infiltrates: Lymphocytes, plasma cells, macrophages. Apoptotic & necrotic cells Healing is also taking place by formation of granulation tissue, composed of cells (macrophages and fibroblasts) proliferating capillaries 33 Granulomatous inflammation Distinctive chronic inflammatory reaction characterised by formation of granulomas. Composed of multinucleate giant cells (macrophages which have joined together) surrounded by lymphocytes a fibrous rim Sometimes with central necrosis (i.e. in tuberculosis). Archetypal granulomatous disease: tuberculosis Other causes of granulomatous disease Bacteria (leprosy, syphilis, cat-scratch disease), parasites (schistosomiasis) or fungi (cryptococcosis) Inorganic material: silicosis, foreign-body Janeway’s Immunobiology, 10th edition Unknown: sarcoidosis, Crohn’s disease 34 Tuberculosis & Granulomatous Inflammation Caused by the bacterial organism Mycobacterium tuberculosis. Characterised granulomatous inflammation with a central region of caseating (cheese-like) material. Caseous necrosis caused by killing of M. tuberculosis-infected macrophages by activated cytotoxic T cells, leading to destruction of surrounding tissue. Organism visualised in body fluids and tissues using Ziehl-Neelsen stain. Janeway’s Immunobiology, 10th edition 35 Immune mediated causes of chronic inflammation: Autoimmune and “unknown” causes Autoimmunity occurs when there is a breakdown of immunological tolerance – the ability of the body to distinguish self from non-self. Usually there is production of an autoantibody which attack selfantigens and T helper cells involved. 36 Outcomes of chronic inflammation Regeneration: replacement of injured cells with cells of the same type. Resolution: complete return to normal structure and function. Regeneration + Resolution à sometimes referred to as Restitution. Repair: tissue architecture and function restored, involving Regeneration: proliferation of undamaged residual cells with the ability to divide Scar formation: deposition of connective (fibrous) tissue if injury is too severe or if the injured tissue is incapable of regeneration, with potential fibrosis (scar tissue) as a result Permanent tissue loss. 37 Wound Healing A wound is a circumscribed 1. 2. 3. 4. (defined) injury caused by an external force, sometimes associated with disruption of structure and function Wound healing occurs through a combination of regeneration and repair. 4 overlapping phases 38 Wound Healing: Phase I and II Haemostasis: vasoconstriction, platelet aggregation, thrombus formation, +/- pressure treatment via stitching etc. Inflammatory phase: neutrophils move in & start clearing debris, chemotaxins are released, macrophages move in, clear debris, organise cells for proliferative phase by secreting cytokines, growth factors etc. 39 Wound Healing III Proliferative phase: can tissue regenerate? Cells capable of proliferation include: Labile cells: continuously dividing cells, e.g. epithelial cells. Stable cells: not continuously dividing, but can replicate when necessary, e.g. hepatocytes, renal tubule cells. Cells not capable of proliferation: Permanent cells do not replicate because have left cell cycle. If they die, wound healing is by repair, or tissue shrinks (such in the brain). Cardiac and skeletal myocytes, neurones in brain and peripheral nerves are all permanent cells. If regeneration cannot occur injured cells are replaced by granulation tissue 40 Angiogenesis, part of proliferative phase Formation of new blood vessels in response to chemical stimuli Important in wound healing and tumour growth. Processes involved: a. Enzymatic degradation of basement membranes of parent vessels. b. Migration of endothelial cells towards stimulus. c. Proliferation of endothelial cells into cords. d. Maturation and lumen formation (initially leaky). 41 Wound Healing IV 4. Remodelling Macrophages remove debris, Increased amounts of collagen are laid down, Vessels disappear, Collagen becomes cross-linked, Myofibroblasts contract, Fibrous scar develops. 42 Healing by primary intention Clean linear wound e.g. laceration or surgical incision. Edges can be brought together easily. 43 Healing by secondary intention Open wound with tissue loss and jagged edges e.g. chronic ulcer, burn or abscess. Edges cannot be approximated. Healing occurs from below. 44 Factors affecting wound healing 45 Complications of wound healing Dehiscence (splitting apart). Infection. Skin discolouration. Hypertrophic scar e.g. keloid (thickened scar). Incisional hernia (when internal part of body pushes against thin scar tissue, stretching it and causing a bulge). Contractures (contraction of scars during remodelling). Adhesions with the abdomen e.g. bowel obstruction. 46 Acute Inflammation vs Chronic Inflammation - ACUTE Inflammation: - an immediate inflammatory response to injury. - a finite (temporary) inflammatory process that can last minutes, hours, days or maybe weeks until resolution. - failure of acute inflammation to resolve can result in chronic inflammation. - CHRONIC Inflammation: - a prolonged period of inflammation largely caused by uncontrolled acute inflammation that has failed to resolve itself. - can last months to years. - implicated in development of chronic diseases (e.g. diabetes) and cancer. 47