Ch 3 inflammation and repair

This is a presentation on the topic of Inflammation and repair, prepared by Dr Ashish Jawarkar, he is MD in pathology and a teacher at Parul institute of Medical sciences and research Vadodara.

1. INFLAMMATION AND REPAIR CHAPTER 3 DR. ASHISH JAWARKAR, MD

2. OVERVIEW Definition Brief introduction Harmful consequences of misdirected inflammation Causes First step of inflammation – acute and chronic Acute inflammation Steps Blood vessel reactions Leucocyte recruitment Clearing of offending agent Termination of response Mediators of acute inflammation Morphologic patterns of acute inflammation Outcomes of acute inflammation

3. OVERVIEW Chronic inflammation Causes Morphological patterns of chronic inflammation Mediators of chronic inflammation Granulomatous inflammation Systemic effects of inflammation Tissue repair Types Repair by regeneration Repair by connective tissue deposition (scar formation) Factors that influence tissue repair Selected examples of tissue repair Skin healing Healing in parenchymal organs Abnormalities in tissue repair

4. z DEFINITION

5. z DEFINITION

6. z BRIEF INTRODUCTION

7. BRIEF INTRODUCTION Acute inflammation The initial, rapid response to infections and tissue damage is called acute inflammation . It typically develops within minutes or hours and is of short duration, lasting for several hours or a few days; its main characteristics are the exudation of fluid and plasma proteins (edema) and the emigration of leukocytes, predominantly neutrophils (also called polymorphonuclear leukocytes). When acute inflammation achieves its desired goal of eliminating the offenders, the reaction subsides. Acute inflammation is one of the reactions of the type of host defense known as innate immunity

8. BRIEF INTRODUCTION Chronic inflammation If acute inflammation fails to clear the stimulus, the reaction can progress to a protracted phase that is called chronic inflammation . Chronic inflammation is of longer duration and is associated with more tissue destruction, the presence of lymphocytes and macrophages, the proliferation of blood vessels, and the deposition of connective tissue. Chronic inflammation is more prominent in the reactions of adaptive immunity

9. z 1. 2. 3. 4. 5.

10. z HARMFUL EFFECTS OF INFLAMMATION

11. HARMFUL EFFECTS OF INFLAMMATION Protective inflammatory reactions to infections are often accompanied by local tissue damage and its associated signs and symptoms (e.g., pain and functional impairment). Typically, however, these harmful consequences are self-limited. In contrast, there are many diseases in which the inflammatory reaction is misdirected (e.g., against self tissues in autoimmune diseases), occurs against normally harmless environmental substances (e.g., in allergies) Following table gives a list of some common diseases caused due to inflammation

12. z CAUSES

13. CAUSES OF INFLAMMATION Infections - bacterial, viral, fungal, parasitic Tissue necrosis – due to ischemia, trauma, physical or chemical injury Foreign bodies Exogenous - splinters, dirt, sutures Endogenous - urate crystals (in the disease gout), Cholesterol crystals (in atherosclerosis), and lipids (in obesity-associated metabolic syndrome) Immune reactions – autoimmune diseases or allergy

14. z FIRST STEP IN INFLAMMATION

15. z FIRST STEP IN INFLAMMATION (RECOGNITION OF MICROBES/DAMAGED CELLS) Innate immunity recognizes foreign antigens (microbes) through receptors on the plasma membranes of epithelial cells, dendritic cells, macrophages and leucocytes Recognition of tissue damage is through factors that are released after damage, such as – uric acid released after DNA break down, ATP – due to mitochondria damage. These and such products activate what are called inflammasomes ( cystosolic complexes) that release IL-1. This IL-1 is thought to be responsible for gout and ATH.

16. z ACUTE INFLAMMATION

17. Acute inflammation Steps Blood vessel reactions Leucocyte recruitment Clearing of offending agent Termination of response Mediators of acute inflammation Morphologic patterns of acute inflammation Outcomes of acute inflammation

18. z STEPS IN ACUTE INFLAMMATION

19. z STEPS IN ACUTE INFLAMMATION

20. 1. BLOOD VESSEL REACTIONS The vascular reactions of acute inflammation consist of changes in the flow of blood Changes in the permeability of vessels both designed to maximize the movement of plasma proteins and leukocytes out of the circulation and into the site of infection or injury.

21. z 1. BLOOD VESSEL REACTIONS A. CHANGES IN FLOW OF BLOOD Vasodilatation Stasis and accumulation of leucocytes, principally neutrophils along the endothelium

22. z 1. BLOOD VESSEL REACTIONS B. INCREASED VASCULAR PERMEABILITY Endothelial contraction/retraction Endothelial injury Transcytosis

23. z STEPS IN ACUTE INFLAMMATION

24. 2. LEUCOCYTE RECRUITMENT AT SITE OF INJURY The journey of leukocytes from the vessel lumen to the site of injury can be divided into sequential phases In the lumen: margination, rolling, and adhesion to endothelium . Migration across the endothelium and vessel wall Migration in the tissues toward a chemotactic stimulus

25. A. Margination, rolling, and adhesion to endothelium Margination white cells assume a peripheral position along the endothelial surface Rolling Subsequently, leukocytes adhere transiently to the endothelium, detach and bind again, thus rolling on the vessel wall (Selectins) Adhesion The cells finally come to rest at some point where they adhere firmly (Integrins) 2. LEUCOCYTE RECRUITMENT AT SITE OF INJURY L selectin

26. B. Migration across the endothelium and vessel wall (diapedesis) 2. LEUCOCYTE RECRUITMENT AT SITE OF INJURY

27. C. Migration in the tissues toward a chemotactic stimulus (Chemotaxis) 2. LEUCOCYTE RECRUITMENT AT SITE OF INJURY

28. z STEPS IN ACUTE INFLAMMATION

29. Phagocytosis involves three sequential steps recognition and attachment of the particle to be ingested by the leukocyte; engulfment , with subsequent formation of a phagocytic vacuole; and killing or degradation of the ingested material (by ROS and other lysosomal enzymes) PHAGOCYTOSIS & KILLING OF OFFENDING AGENT

30. Neutrophilic lysosomes contain two types of granules Smaller specific (or secondary) granules contain lysozyme, collagenase, gelatinase, lactoferrin, plasminogen activator, histaminase, and alkaline phosphatase. The larger azurophil (or primary) granules contain myeloperoxidase, bactericidal factors (lysozyme, defensins), acid hydrolases, and a variety of neutral proteases (elastase, cathepsin G, nonspecific collagenases, proteinase 3). Acid proteases degrade bacteria and debris Neutral proteases are capable of degrading various extracellular components, such as collagen, basement membrane, fibrin, elastin, and cartilage PHAGOCYTOSIS & KILLING OF OFFENDING AGENT

31. z STEPS IN ACUTE INFLAMMATION

32. 4. TERMINATION OF RESPONSE Removal of mediators of inflammation - mediators of inflammation are produced in rapid bursts, only as long as the stimulus persists, have short half-lives, and are degraded after their release. Short half life of inflammatory cells – inflammatory cells die by apoptosis within a few hours after leaving the blood. Stop signals - These include antiinflammatory cytokines, including transforming growth factor-β (TGF-β) and IL-10, from macrophages and other cells.

33. LEUCOCYTE MEDIATED TISSUE INJURY Collateral damage: As part of a normal defence reaction against infectious microbes, when adjacent tissues suffer collateral damage. Difficult to eradicate infections: In some infections that are difficult to eradicate, such as tuberculosis and certain viral diseases, the prolonged host response contributes more to the pathology than does the microbe itself. Autoimmunity: When the inflammatory response is inappropriately directed against host tissues, as in certain autoimmune diseases. Allergy: When the host reacts excessively against usually harmless environmental substances, as in allergic diseases, including asthma. 4. TERMINATION OF RESPONSE

34. z MEDIATORS OF ACUTE INFLAMMATION

35. MEDIATORS OF ACUTE INFLAMMATION The mediators of inflammation are the substances that initiate and regulate inflammatory reactions. Some chief mediators with their actions is summarised below. We will discuss them in detail in slides that follow - Vasoactive amines - mainly histamine and serotonin: vasodilation and increased vascular permeability Arachidonic acid metabolites (prostaglandins and leukotrienes): several forms exist and are involved in vascular reactions, leukocyte chemotaxis, and other reactions of inflammation; antagonized by lipoxins Cytokines: proteins produced by many cell types; usually act at short range; mediate multiple effects, mainly in leukocyte recruitment and migration; principal ones in acute inflammation are TNF, IL-1, and chemokines INTRODUCTION

36. Complement system proteins: Activation of the complement system by microbes or antibodies leads to the generation of multiple breakdown products, which are responsible for leukocyte chemotaxis, opsonization, and phagocytosis of microbes and other particles, and cell killing Kinins: produced by proteolytic cleavage of precursors; mediate vascular reaction, pain MEDIATORS OF ACUTE INFLAMMATION INTRODUCTION

37. Histamine Richest sources of histamine are the mast cells that are normally present in the connective tissue adjacent to blood vessels Released by mast cells in response to variety of stimuli such as – Heat, cold or trauma Hypersensitivity (allergy) Anaphylatoxins (C3a and C5a) Histamine causes dilation of arterioles and increases the permeability of venules Its vasoactive effects are mediated mainly via binding to receptors, called H 1 receptors, on microvascular endothelial cells MEDIATORS OF ACUTE INFLAMMATION A. VASOACTIVE AMINES – HISTAMINE AND SEROTONIN

38. Serotonin Serotonin (5-hydroxytryptamine) is a preformed vasoactive mediator present in platelets and certain neuroendocrine cells It is also a vasoconstrictor A. VASOACTIVE AMINES – HISTAMINE AND SEROTONIN MEDIATORS OF ACUTE INFLAMMATION

39. B. ARACHIDONIC ACID METABOLITES – PROSTAGLANDINS AND LEUKOTRIENES The lipid mediators prostaglandins and leukotrienes are produced from arachidonic acid (AA) present in membrane phospholipids MEDIATORS OF ACUTE INFLAMMATION

40. Cytokines Cytokines are proteins produced by many cell types (principally activated lymphocytes, macrophages, and dendritic cell, but also by endothelial, epithelial, and connective tissue cells) that mediate and regulate immune and inflammatory reactions Following table summarises some chief cytokines involved in inflammation and their actions MEDIATORS OF ACUTE INFLAMMATION

41. C. Cytokines MEDIATORS OF ACUTE INFLAMMATION

42. C. Cytokines MEDIATORS OF ACUTE INFLAMMATION

43. Chemokines are a family of small (8 to 10 kD ) proteins that act primarily as chemo attractants for specific types of leukocytes Role of chemokines In acute inflammation stimulate leukocyte attachment to endothelium stimulate migration (chemotaxis) of leukocytes Maintenance of tissue architecture Some chemokines are produced constitutively in tissues and are sometimes called homeostatic chemokines . These organize various cell types in different anatomic regions of the tissues, such as T and B lymphocytes in discrete areas of the spleen and lymph nodes D. Chemokines MEDIATORS OF ACUTE INFLAMMATION

44. The complement system is a collection of soluble proteins and membrane receptors that function mainly in host defence against microbes and in pathologic inflammatory reactions The system consists of more than 20 proteins, some of which are numbered C1 through C9 Complement proteins are present in inactive forms in the plasma, and many of them are activated to become proteolytic enzymes that degrade other complement proteins, thus forming an enzymatic cascade The critical step in complement activation is the proteolysis of the third (and most abundant) component, C3 E. Complement system MEDIATORS OF ACUTE INFLAMMATION

45. E. Complement system MEDIATORS OF ACUTE INFLAMMATION

46. E. Complement system MEDIATORS OF ACUTE INFLAMMATION

47. z MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION

48. MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION SEROUS INFLAMMATION FIBRINOUS INFLAMMATION PURULENT INFLAMMATION ULCERS

49. 1. Serous inflammation Serous inflammation is marked by the exudation of cell poor fluid into spaces created by cell injury or into body cavities lined by the peritoneum, pleura, or pericardium. Typically, the fluid in serous inflammation is not infected by destructive organisms and does not contain large numbers of leukocytes (which tend to produce purulent inflammation, described later). In body cavities the fluid may be derived from the plasma (as a result of increased vascular permeability) or from the secretions of mesothelial cells (as a result of local irritation); accumulation of fluid in these cavities is called an effusion . (Effusions also occur in noninflammatory conditions, such as reduced blood outflow in heart failure, or reduced plasma protein levels in some kidney and liver diseases.) The skin blister resulting from a burn or viral infection represents accumulation of serous fluid within or immediately beneath the damaged epidermis of the skin MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION

50. With greater increase in vascular permeability, large molecules such as fibrinogen pass out of the blood, and fibrin is formed and deposited in the extracellular space. A fibrinous exudate is characteristic of inflammation in the lining of body cavities, such as the meninges, pericardium and pleura. Conversion of the fibrinous exudate to scar tissue (organization) within the pericardial sac leads to obliteration of the pericardial space. 2. Fibrinous inflammation MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION

51. Purulent inflammation is characterized by the production of pus, an exudate consisting of neutrophils, the liquefied debris of necrotic cells, and edema fluid Abscesses are localized collections of purulent inflammatory tissue caused by suppuration buried in a tissue, an organ, or a confined space 3. Purulent inflammation (Abscess) MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION

52. An ulcer is a local defect, or excavation, of the surface of an organ or tissue that is produced by the sloughing (shedding) of inflamed necrotic tissue Ulcerations are best exemplified by peptic ulcer of the stomach or duodenum, in which acute and chronic inflammation coexist. During the acute stage there is intense polymorphonuclear infiltration and vascular dilation in the margins of the defect. With chronicity, the margins and base of the ulcer develop fibroblastic proliferation, scarring, and the accumulation of lymphocytes, macrophages, and plasma cells. 4. Ulcers MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION

53. z OUTCOMES OF ACUTE INFLAMMATION

54. OUTCOMES OF ACUTE INFLAMMATION

55. z CHRONIC INFLAMMATION

56. CHRONIC INFLAMMATION Causes Morphological patterns of chronic inflammation Mediators of chronic inflammation Granulomatous inflammation

57. z CAUSES OF CHRONIC INFLAMMATION

58. CAUSES Persistent infections – by microorganisms that are difficult to eradicate, such as mycobacteria and certain viruses, fungi, and parasites. These organisms often evoke an immune reaction called delayed-type hypersensitivity. The inflammatory response sometimes takes a specific pattern called a granulomatous reaction Autoimmunity – Autoantigens evoke a self-perpetuating immune reaction that results in chronic tissue damage and inflammation; examples of such diseases are rheumatoid arthritis and multiple sclerosis Allergy – Immune responses against common environmental substances are the cause of allergic diseases , such as bronchial asthma Prolonged exposure to toxic agents - Eg silicosis, atherosclerosis

59. z MORPHOLOGIC PATTERNS

60. z MORPHOLOGIC PATTERNS Infiltration with mononuclear cells, which include macrophages, lymphocytes, and plasma cells Tissue destruction, induced by the persistent offending agent or by the inflammatory cells Attempts at healing by connective tissue replacement of damaged tissue, accomplished by angiogenesis (proliferation of small blood vessels) and, in particular, fibrosis ACUTE VS CHRONIC INFLAMMATION

61. z MEDIATORS OF CHRONIC INFLAMAMATION

62. MEDIATORS OF CHRONIC INFLAMMATION Macrophages Lymphocytes Eosinophils Mast cells Neutrophils

63. Macrophages Cells derived from monocytes – part of mononuclear phagocyte system Examples normally diffusely scattered in most connective tissues. liver (where they are called Kupffer cells), spleen and lymph nodes (called sinus histiocytes), central nervous system (microglial cells), and lungs (alveolar macrophages) MEDIATORS OF CHRONIC INFLAMMATION

64. The dominant cells in most chronic inflammatory reactions are macrophages, which contribute to the reaction by secreting cytokines and growth factors that act on various cells, by destroying foreign invaders and tissues, and by activating other cells, notably T lymphocytes Macrophages MEDIATORS OF CHRONIC INFLAMMATION

65. There are two major pathways of macrophage activation, called classical and alternative MEDIATORS OF CHRONIC INFLAMMATION Macrophages Produced by T lymphocytes

66. Microbes and other environmental antigens activate T lymphocytes, which amplify and propagate chronic inflammation There are three subsets of CD4+ T cells that secrete different types of cytokines and elicit different types of inflammation. TH1 cells produce the cytokine IFN-γ, which activates macrophages by the classical pathway. TH2 cells secrete IL-4, IL-5, and IL-13, which recruit and activate eosinophils and are responsible for the alternative pathway of macrophage activation. TH17 cells secrete IL-17 and other cytokines, which induce the secretion of chemokines responsible for recruiting neutrophils (and monocytes) into the reaction. Lymphocytes MEDIATORS OF CHRONIC INFLAMMATION

67. Lymphocytes MEDIATORS OF CHRONIC INFLAMMATION

68. Eosinophils are abundant in immune reactions mediated by IgE and in parasitic infections Mast cells release mediators, such as histamine and prostaglandins Neutrophils play a part in acute on chronic reactions – In osteomyelitis, a neutrophilic exudate can persist for many months. Neutrophils are also important in the chronic damage induced in lungs by smoking Eosinophils, Mast cells and Neutrophils MEDIATORS OF CHRONIC INFLAMMATION

69. z GRANULOMATOUS INFLAMMATION

70. z GRANULOMATOUS INFLAMMATION Granulomatous inflammation is a form of chronic inflammation characterized by collections of activated macrophages, often with T lymphocytes, and sometimes associated with central necrosis The activated macrophages may develop abundant cytoplasm and begin to resemble epithelial cells, and are called epithelioid cells . Some activated macrophages may fuse, forming multinucleate giant cells ( Langhan’s ) This is a type of immune granuloma – produced when infecting agent is difficult to eradicate

71. z FOREIGN BODY GRANULOMA incited by relatively inert foreign bodies foreign body granulomas form around materials such as talc (associated with intravenous drug abuse) sutures, or other fibres that are large enough to preclude phagocytosis by a macrophage

72. z

73. z SYSTEMIC EFFECTS OF INFLAMMATION

74. z SYSTEMIC EFFECTS OF INFLAMMATION

75. z TISSUE REPAIR

76. z Tissue Repair

77. Repair Vs Regeneration Regeneration some tissues are able to replace the damaged components and essentially return to a normal state; this process is called regeneration Tissues whose cells retain the capacity to proliferate, for example, in the rapidly dividing epithelia of the skin and intestines, and the liver can undergo regeneration Repair (scar formation) If the injured tissues are incapable of complete restitution, or if the supporting structures of the tissue are severely damaged, repair occurs by the laying down of connective (fibrous) tissue

78. Concept of Regeneration Regeneration of the liver is a classic example of repair by regeneration. It is triggered by cytokines and growth factors produced in response to loss of liver mass and inflammation. In different situations, regeneration may occur by proliferation of surviving hepatocytes or repopulation from progenitor cells (stem cells), these progenitor cells have been called oval cells because of the shape of their nuclei. Some of these progenitor cells reside in specialized niches called canals of Hering

79. Repair (by connective tissue deposition; Scar formation) Scar formation is a response that “patches” rather than restores the tissue The term scar is most often used in connection to wound healing in the skin, but may also be used to describe the replacement of parenchymal cells in any tissue by collagen, as in the heart after myocardial infarction

80. Steps in repair Angiogenesis Angiogenesis is the formation of new blood vessels, which supply nutrients and oxygen needed to support the repair process Formation of granulation tissue Migration and proliferation of fibroblasts and deposition of loose connective tissue, together with the vessels and interspersed leukocytes, form granulation tissue . The term granulation tissue derives from its pink, soft, granular gross appearance, such as that seen beneath the scab of a skin wound. Remodelling of connective tissue Maturation and reorganization of the connective tissue produce the stable fibrous scar

81. Skin wound healing This is a process that involves both epithelial regeneration and the formation of connective tissue scar Based on the nature and size of the wound, the healing of skin wounds is said to occur by first or second intention Healing by First Intention When the injury involves only the epithelial layer, the principal mechanism of repair is epithelial regeneration One of the simplest examples of this type of wound repair is the healing of a clean, uninfected surgical incision approximated by surgical. The incision causes only focal disruption of epithelial basement membrane continuity and death of relatively few epithelial and connective tissue cells.

82. Skin wound healing Healing by Second Intention When cell or tissue loss is more extensive, such as in large wounds, abscesses, ulceration, and ischemic necrosis (infarction) in parenchymal organs, the repair process involves a combination of regeneration and scarring

83. Healing by first intention Steps 1 st 24 hours – Wounding causes the rapid activation of coagulation pathways, which results in the formation of a blood clot on the wound surface. As dehydration occurs at the external surface of the clot, a scab covering the wound is formed. Neutrophils are seen at the incision margin. They release proteolytic enzymes that begin to clear the debris. Epithelial cell proliferation starts at the edge of the wound 3-7 days – Neutrophils have been largely replaced by macrophages, and granulation tissue progressively invades the incision space Collagen fibers and fibroblasts are now evident at the incision margins. Epithelial cell proliferation continues, forming a covering approaching the normal thickness of the epidermis.

84. Healing by first intention Steps Weeks – The epidermis recovers its normal thickness The process of “blanching” begins, accomplished by increasing collagen deposition within the incisional scar and the regression of vascular channels By the end of the first month, the scar comprises a cellular connective tissue largely devoid of inflammatory cells and covered by an essentially normal epidermis. However, the dermal appendages destroyed in the line of the incision are permanently lost. The tensile strength of the wound increases with time due to collagen cross linking

85. Healing by second intention Steps Secondary healing differs from primary healing in several respects: The fibrin clot is larger, and there is more exudate and necrotic debris in the wounded area. Inflammation is more intense because large tissue defects have a greater volume of necrotic debris, exudate, and fibrin that must be removed. Larger defects require a greater volume of granulation tissue to fill in the gaps and provide the underlying framework for the regrowth of tissue epithelium. A greater volume of granulation tissue generally results ina greater mass of scar tissue. Wound contraction generally occurs in large surface wounds. The contraction helps to close the wound by decreasing the gap between its dermal edges and by reducing the wound surface area. Contraction is mediated by a network of myofibroblasts , which are modified fibroblasts exhibiting many of the ultrastructural and functional features of contractile smooth muscle cells.

86. Abnormalities in tissue repair Complications in tissue repair can arise from abnormalities in any of the basic components of the process, including Dehiscence and Ulceration Dehiscence - Dehiscence or rupture of a wound occurs most frequently after abdominal surgery and is due to increased abdominal pressure Ulceration - Wounds can ulcerate because of inadequate vascularization during healing. For example, lower extremity wounds in individuals with atherosclerotic peripheral vascular disease

87. Abnormalities in tissue repair Excessive formation of the repair components Hypertrophic scar - accumulation of excessive amounts of collagen may give rise to a raised scar known as a hypertrophic scar Keloid - if the scar tissue grows beyond the boundaries of the original wound and does not regress, it is called a keloid Exuberant granulation - consisting of the formation of excessive amounts of granulation tissue, which protrudes above the level of the surrounding skin and blocks reepithelialisation ( proud flesh ) Desmoids, or aggressive fibromatoses - E xuberant proliferation of fibroblasts, these neoplasms lie in the interface between benign and malignant Contractures Exaggeration of process of contraction during healing is prone to develop in palms and soles and thorax. Contractures are commonly seen after serious burns and can compromise the movement of joints.