Inflammation

pathology inflammation

1. Inflammation Dr. Dussa Vamshikrishna MD (H)

2. Learning Objectives What is Inflammation? Its Types. Etiology/Causes of Inflammation. Steps of Inflammatory Response. Acute Inflammation- Vascular Events Cellular Events

3. Inflammation: Definition. Inflammation is defined as the local response of living mammalian tissues to injury from any agent. WAR

4. It is a body defense reaction . Eliminates injurious agent, Limits the spread of Injurious Agent. Followed by removal of the necrosed cells and tissues.

5. INJURIOUS AGENTS CAUSING INFLAMMATION:

6. SIGNS OF INFLAMMATION The Roman writer Celsus in 1 st century A.D. named the famous 4 cardinal signs of inflammation as: I) Rubor (Redness) II) Tumor (Swelling) III) Calor (Heat) IV) Dolor (Pain). To these, fifth sign Functio Laesa (loss of function) was later added by Virchow.

7. Steps of Inflammatory Response.- 5 R's 1. Recognition of Injurious Agent. 2. Recruitment of Inflammatory Cells. 3. Removal of Injurious Agent. 4. Regulation of the Inflammatory Response. 5. Resolution/Repair.

8. TYPES OF INFLAMMATION Depending upon the defense capacity of the host and duration of response, inflammation can be classified as ACUTE INFLAMMATION CHRONIC INFLAMMATION

9. Acute Vs Chronic Feature Acute C hronic Onset Rapid; Mins to Hrs. Slow , Takes days Cells Neutrophils Lymphocytes, Macrocytes/Monocytes Tissue Injury Mild, Self Limited Severe, Progressive Signs: Local, Systemic. Prominent Less Prominent

10. ACUTE INFLAMMATION

11. Characteristics of Acute Inflammation: Short Duration- < 2 weeks Early Body Reaction Resolves Quickly It is followed by Healing

12. It can be divided into following two events: I. Vascular events II. Cellular events

13. Events VASCULAR Increased Blood flow to the Injured Area To bring the Cells and Proteins to Site of Injury. Vasodilatation and Increased Vascular Permeability of the Blood Vessels near the Site. CELLULAR Recruitment of the Leukocytes Activation of Leucocytes- which will destruct the invaders, produce the mediators. Phagocytosis.

14. I. VASCULAR EVENTS Alteration in the microvasculature (arterioles, capillaries and venules) is the earliest response to tissue injury. These alterations include: Haemodynamic changes. Changes in Vascular Permeability.

15. A. Haemodynamic Changes: Sequence of changes are under: Transient vasoconstriction of arterioles. Immediate vascular response. 3-5 SECONDS FOR MILD INJURY 5 MINS FOR SEVERE INJURY

16. 2. Persistent Progressive Vasodilatation: Mainly Arterioles, less extent Venules and Capillaries. Occurs after 30 mins/ Half an Hour of Injury. Causes increased blood volume in the injured area Responsible for the signs: RUBOR AND CALOR

17. 3. Progressive Vasodilatation- Increased Local Hydrostatic Pressure: Results in transudation of fluid into Extracellular Space. This leads to local swelling- TUMOR

18. 4. Stasis of Microcirculation: Increased concentration of RED CELLS Leading to Increased Viscosity of the Blood at the site of Inflammation.

19. 5. Leucocytic Margination: Peripheral orientation of leucocytes (mainly neutrophils) along the vascular endothelium. The leucocytes stick to the vascular endothelium briefly, and then move and migrate through the gaps between the endothelial cells into the extravascular space. This process is known as emigration.

20. Triple Response /Red Line Response It demonstrates features of haemodynamic changes in inflammation by Lewis experiment. Lewis induced the changes in the skin of inner aspect of forearm by firm stroking with a blunt point.

21. The reaction so elicited is known as Triple Response or Red Line Response consisting of the following. Red line Flare Wheal

22. The reaction so elicited is known as Triple Response or Red Line Response consisting of the following. 1 ) Red line appears within a few seconds after stroking and is due to local vasodilatation of capillaries and venules.

23. 2) Flare: Bright reddish appearance or flush surrounding the red line and results from vasodilatation of the adjacent arterioles.

24. 3)Wheal : Swelling or Oedema of the surrounding skin occurring due to transudation of fluid into the extravascular space.

25. These features, thus, elicit the classical signs of inflammation— Redness, Heat And Swelling, to which fourth feature, pain, has been added.

26. 2. Altered Vascular Permeability Increased vascular permeability in acute inflammation by which normally non-permeable endothelial layer of microvasculature becomes leaky can have following patterns and mechanisms.

27. MECHANISMS OF INCREASED VASCULAR PERMEABILITY: i) Contraction of Endothelial cells. ii) Mild Endothelial Damage. iii) Leucocyte-mediated endothelial injury. iv ) Leakiness in neovascularisation / Transcytosis

28. 1) Contraction of Endothelial cells. Most common mechanism. Affects Venules exclusively while capillaries and arterioles remain unaffected. Temporary in nature. Mediated by the histamine, bradykinin and other chemical mediators. Reversible. Short duration (15-30 minutes). Eg: Thermal injury of skin

29. Normal Venule

30. Leaky Venule

31. 2. Mild Endothelial Damage . Affects Venules and Capillaries . Seen in Burns/Sun Burns/UV radiation. Mediated by cytokines such as Interleukin-1 (IL-1) and tumour necrosis factor (TNF)-a. Seen after 4-6 hours following injury and lasts for several hours to days.

32. Damaged Venule

33. iii) Leucocyte -mediated endothelial injury. Adherence of leucocytes to the endothelium at the site of inflammation may result in activation of leucocytes. The activated leucocytes release proteolytic enzymes and toxic oxygen species which may cause endothelial injury and increased vascular leakiness. This form of increased vascular leakiness affects mostly venules and is a late response.

34. Damaged Venule

35. iv) Leakiness in Neovascularisation/Transcytosis. Increased transport of Fluids and Proteins across the intracellular channels ( Transcytosis) . The newly formed capillaries under the influence of Vascular Endothelial Growth Factor (VEGF) during the process of repair and in tumours are excessively leaky.

36. Transcytosis.

37. II. CELLULAR EVENTS The cellular phase of inflammation consists of 2 processes: 1. Exudation of Leucocytes. (Influx to the site of Injury) 2. Phagocytosis . (Ingestion and Destruction of injurious Agents)

38. 1. Exudation of Leucocytes. The escape of leucocytes from the lumen of microvasculature to the interstitial tissue is the most important feature of inflammatory response. In acute inflammation, polymorphonuclear neutrophils (PMNs) comprise the first line of body defense, followed later by monocytes and macrophages.

39. CHANGES LEADING TO MIGRATION OF LEUCOCYTES: Margination and Pavementing of Blood Elements. Rolling and Adhesion. Emigration. Chemotaxis .

40. Margination and Pavementing of Blood Elements. Rolling and Adhesion Emigration.

41. Margination and Pavementing of Blood Elements. VASODILATATION INCREASED RATE OF FLOW OF BLOOD CHANGES IN THE NORMAL AXIAL FLOW OF BLOOD i.e. central stream of cells widens and peripheral plasma zone becomes narrower because of loss of plasma by exudation. This phenomenon is known as MARGINATION . STASIS REDISTRIBUTION OF NEUTROPHILS OF THE CENTRAL COLUMN TO THE VESSEL WALL : PAVEMENTING .

42. NORMAL AXIAL FLOW OF BLOOD

43. MARGINATION . PAVEMENTING .

44. II. Rolling and Adhesion Peripherally marginated and pavemented neutrophils slowly roll over the endothelial cells lining the vessel wall (rolling phase).

45. ROLLING SELECTINS

46. ROLLING SELECTINS

47. ROLLING SELECTINS

48. ROLLING SELECTINS

49. CELL ADHESION MOLECULES (CAMS) EXPRESSED ON ENDOTHELIAL CELLS GETS ACTIVATED BY TNF & IL-1 AND BRING ABOUT ROLLING OF LEUCKOCYTES (WEAK BONDING) SELECTINS (3 types of Selectins) P- SELECTIN (CD62)- INVOLVED IN ROLLING E-SELECTIN (E-CAM) - INVOLVED IN BOTH ROLLING AND ADHESION L-SELECTIN (L-CAM) - ON THE SURFACE OF LYMPHOCYTES AND NEUTROPHILS (HELPS IN HOMING OF LEUKOCYTES TO LYMPH NODES)

50. ADHESION Integrins Integrin Ligand This is followed by transient bond between the leucocytes and endothelial cells becoming firmer - ADHESION PHASE.

51. Integrins proteins gets activated (by IL-1, TNF) during the process of loose and transient adhesions between endothelial cells and leucocytes .

52. III. Emigration. After sticking of neutrophils to endothelium, they move through a suitable site between the endothelial cells by cytoplasmic pseudopods .

53. Neutrophils lodged between the endothelial cells and basement membrane cross the basement membrane by damaging it locally with secreted collagenases and escape out into the extravascular space; this is known as EMIGRATION.

54. Simultaneous to emigration of leucocytes, escape of red cells through gaps between the endothelial cells, diapedesis , takes place. diapedesis

55. IV. Chemotaxis The transmigration of leucocytes after crossing several barriers to reach the interstitial tissues is a chemotactic factor mediated process called chemotaxis .

56. The following agents act as potent chemotactic substances for neutrophils: i ) Leukotriene B4 (LT-B4) ii) Components of complement system (C5a and C3a in particular) iii) Cytokines ( Interleukins , in particular IL-8) iv) Soluble bacterial products

57. 2. Phagocytosis. Phagocytosis is defined as the process of engulfment of solid particulate material by the cells (cell-eating). The cells performing this function are called phagocytes.

58. There are 2 main types of phagocytic cells: i ) Polymorphonuclear neutrophils (PMNs) which appear early in acute inflammatory response, sometimes called as microphages. ii) Circulating monocytes and fixed tissue mononuclear phagocytes, commonly called as macrophages.

59. Phagocytosis of the microbe by polymorphs and macrophages involves the following 3 steps: Recognition and attachment. Engulfment. Killing and degradation.

60. Recognition and Attachment: Special receptors on the phagocytes recognize the microbes/necrotic cells. Phagocytic Receptors: Mannose Receptors Scavenger Receptors Opsonin Receptors- IgG Opsonins , C3b Opsonin , Lectins .

61. ( opsonin )

62. 2. Engulfment. Microbes recognized by receptors are ready to be engulfed by PMN/Macrophage Cytoplasmic pseudopods of Phagocytes formed from activated actin filaments of cell wall will engulf the microbe Phagocytic vacuole ( Phagosome ) is formed in the cytoplasm from the detached cell membrane which previously engulfed microbe by its pseudopods. The phagosome fuses with one or more lysosomes of the cell and form bigger vacuole called phagolysosome .

63. 3. Killing and degradation. Destruction of Phagocytosed microbes/Dead cells by following mechanisms: A . Intracellular mechanisms : ( in Phagolysosomes ) 1. Oxidative Bactericidal Mechanism a. By Oxygen Free Radicals. Myeloperoxidase (MPO)-dependent Myeloperoxidase (MPO)-independent b. By Lysosomal granules. 2. Non-oxidative Bactericidal Mechanism B. Extracellular mechanisms:

64. A. INTRACELLULAR MECHANISMS Oxidative Bactericidal Mechanism: a. By Oxygen Free Radicals. Microbes are killed by the production of Reactive Oxygen Metabolites (O - 2 , H 2 O 2 , OH - , HOCl, HOI, HOBr). Reactive Oxygen Metabolites are produced by the action of NADPH oxidase (which is present in the membrane of the phagosome and lysosome) on the molecular OXYGEN.

65. OXYGEN (O 2 ) O 2 – (SUPEROXIDE ANION) NADPH oxidase REDUCTION NADPH NADP + H + 2H + + O 2 – H 2 O 2 (Hydrogen peroxide) (NOT A POTENT ANTIMICROBIAL AGENT)

66. The potency of H 2 O 2 is increased in phagocytes by the action of enzyme MYELOPEROXIDASE on H 2 O 2 in the presence of halides (chloride, iodide) to more potent form hypohalous acid ( HOCl , HOI, HOBr ). THIS IS CALLED AS MPO-dependent killing. Seen in Neutrophils.

67. Mature macrophages lack the enzyme MPO and they carry out bactericidal activity by producing OH – ions and superoxide singlet oxygen ( O - ) from H 2 O 2 in the presence of O 2 - (Haber-Weiss reaction) or in the presence of Fe++ (Fenton reaction). This is called MPO-independent killing. Hydroxyl radical superoxide singlet oxygen

68. b. By lysosomal granules: Lysosomal granules in lysosomes release enzymes like protease, trypsinase , phospholipase , and alkaline phosphatase into phagosome and degrades the protein component of microbes and bring about the lysis along with the oxygen free radicals.

69. 2. Non-oxidative Bactericidal Mechanism: Some agents released from the granules of phagocytic cells do not require oxygen for bactericidal activity. Enzymes like lipases, proteases, DNAases cause lysis of microbe within phagosome without help of oxygen free radicals. Nitric oxide, a free radical and potent microbial agent similar to oxygen free radicals produced by macrophages kills the microbes.

70. B. Extracellular mechanisms: Immune-mediated lysis of microbes takes place outside the cells by mechanisms of cytolysis, antibody mediated lysis and by cell-mediated cytotoxicity

71. REGULATION OF INFLAMMATION The onset of inflammation has potentially damaging influence on the host tissues as evident in hypersensitivity conditions. Such self-damaging effects are kept in check by the host regulatory mechanisms in order to resolve inflammation.

72. Agents which check the inflammation: Acute phase reactants. Glucosteroids. Free cytokine receptors. Anti-inflammatory chemical mediators.

73. Acute Phase Reactant proteins. APR proteins play a major role is to protect the normal cells from harmful effects of toxic molecules generated in inflammation and to clear away the waste material. The APR are synthesised mainly in the liver, and to some extent in macrophages. APR along with systemic features of fever and leucocytosis is termed ‘acute phase response’. Deficient synthesis of APR leads to severe form of disease in the form of chronic and repeated inflammatory responses.

74. CELLULAR PROTECTION FACTORS α 1-antitrypsin, α 1-chymotrypsin, α 2-antiplasmin, plasminogen activator REPLACES THE CONSUMED FACTORS IN COAGULATION Fibrinogen, Plasminogen , Von Willebrand Factor, Factor VIII