Inflammation

inflammation

1. INFLAMMATION DR KARUNA SHARMA PG 1 ST YEAR

2. CONTENTS DEFINITION TYPES OF INFLAMMATION COMPONENTS OF INFLAMMATION HISTORICAL HIGHLIGHTS ACUTE INFLAMMATION DEFINITION STIMULI FOR ACUTE INFLAMMATION VASCULAR CHANGES CELLULAR EVENTS margination & rolling adhesion & transmigration chemotaxis &activation phagocytosis & degranulation leukocyte induced tissue injury defects in leukocyte function

3. CHEMICAL MEDIATORS OF INFLAMMATION OUTCOMES OF ACUTE INFLAMMATION MORPHOLOGIC PATTERNS OF ACUTE INFLAMMATION CHRONIC INFLAMMATION SYSTEMIC EFFECTS OF INFLAMMATION CONSEQUENCES OF DEFECTIVE OR EXCESSIVE INFLAMMATION

4. DEFINITION Inflammation is a complex reaction to injurious agents such as microbes and damaged, usually necrotic, cells that consists of vascular responses ,migration and activation of leukocytes, and systemic reactions. Kumar,Abbas,Fausto:Robbins and Cotran Pathological basis of disease.Pennysilvenya,Elsevier,1999

5. Inflammation is divided into two types – 1. Acute inflammation 2. Chronic inflammation

6. ACUTE INFLAMMATION Is the immediate & early response to injury. Is of relatively short duration. Due to neutrophilic leukocytic accumulation. CHRONIC INFLAMMATION Is of longer duration in which active inflammation tissue injury & healing proceed simultaneously. Manifested by influx of lymphocytes & macrophages.

7. COMPONENTS OF INFLAMMATION The inflammatory response consists of two main components- a vascular reaction a cellular reaction

8. HISTORICAL HIGHLIGHTS CARDINAL SIGNS Celsus in first century AD,first listed the four signs - Rubor (redness) -Tumor(swelling) - Calor (heat) & -Dolor(pain) -a fifth clinical sign, loss of function( functio lasea ) - Rudolf virchow in seventeenth century. These signs are typically more prominent in acute inflammation than in chronic inflammation

9. ACUTE INFLAMMATION It is a rapid new response to an injurious agent that serves to deliver mediators of host response-leukocytes and plasma proteins-to the site of injury. It is of relatively short duration,lasting for minutes,several hours or a few days .

10. COMPONENTS OF ACUTE INFLAMMATION It has three major components: Alterations in vascular caliber that lead to an increase in blood flow Structural changes in the microvasculature(increased vascular permeability) that permit plasma proteins and leukocytes to leave the circulation. Emigration of the leukocytes from the microcirculation,their accumulation in the focus of injury,and their activation to eliminate the offending agent.

11. STIMULI FOR ACUTE INFLAMMATION Infections( bacterial,viral,parasitic )and microbial toxins Trauma(blunt and penetrating) Physical and chemical agents(thermal injury,e.g.,burns or frostbite;irradiation;some environmental chemicals) Tissue necrosis Foreign bodies( splinters,dirt,sutures ) Immune reactions(called hypersensitivity reactions)

12. VASCULAR CHANGES Changes in vascular flow and caliber begin very early after injury and ,depends on the severity of injury. They occur in the following order- Vasodilation Slowing of the circulation Leukocytic margination

13. VASODILATATION Following an inconstant and transient vasoconstriction of arterioles,lasting a few seconds, vasodilatation occurs. This first involves the arterioles and then results in opening of new capillary beds in the area.Thus comes about the increased blood flow( cause of the heat and the redness .) It is induced by the action of mediators histamine & nitric oxide on vascular smooth muscle.

14. SLOWING OF THE CIRCULATION Vasodilatation is followed by increased permeability of the microvasculature, with the outpouring of protein rich fluid into the extravascular tissues. The latter results in concentration of red cells in small vessels and increased viscosity of blood,reflected by the presence of dilated small vessels packed with red cells & slower blood flow termed stasis .( rubor )

15. LEKOCYTIC MARGINATION As stasis develops peripheral orientation of leukocytes occur,pricipally neutrophils,along the vascular endothelium,a process called leukocytic margination . Leukocytes then stick to the endothelium,at first transiently (rolling), then more avidly and soon they migrate into the interstitial tissue . The time scale of these events is variable .With mild stimuli the stages of stasis may not become apparent until 15 to 20 minutes have elapsed,whereas with severe injury ,stasis may occur in a few minutes,

16. INCREASED VSCULAR PERMEABILITY (vascular leakage) Increased vascular permeability leading to the escape of protein rich fluid into the interstitium is the hallmark of acute inflammation. The loss of protein rich fluid from the plasma reduces the intravascular osmotic pressure and increases the osmotic pressure of the interstitial fluid. Together with the increased hydrostatic pressure due to vasodilatation,this leads to a marked outflow of fluid and its accumulation in the interstitial tissue.This net increase of extravascular fluid is edema.

17. Normal fluid exchange & microvascular permeability are dependent on an intact endothelium. Endothelium becomes leaky in inflammation. Five mechanisms are known.

18. MECHANISMS OF VASCULAR LEAKAGE Endothelial cell contraction Junctional retraction Direct endothelial injury Leukocyte dependent leakage Increased transcytosis Regenerating endothelium

19. 1.ENDOTHELIAL CONTRACTION Endothelial cell contraction,leads to the formation of widened intercellular junctions,or intercellular gaps.This is the most common method of vascular leakage. It is elicited by histamine,bradykinin,leukotrienes and other classes of chemical mediators. It is usually reversible and short-lived,(15-30 minutes)& is thus known as the immediate transient response. This type of leakage mainly affects only venules leaving capillaries and arterioles unaffected.

20. Binding of the mediators to their receptors on endothelial cells activates intracellular signaling pathways that lead to phosphorylation of contractile and cytoskeleton proteins such as myosin. These proteins contract ,leading to contraction of endothelial cells & seperation of intercellular junctions.

21. 2.CYTOSKELETAL AND JUNCTIONAL REORGANIZATION(endothelial retraction) A different mechanism of reversible intercellular leakage,resulting in interendothelial gaps,can be induced in vitro by cytokine mediators,such as – interleukin-1(IL-1), tumor necrosis factor(TNF),and interferon-gamma(INF- ᵧ ). These cytokines increase the vascular permeability by inducing a structural reorganization of the cytoskeleton.

22. Such that the endothelial cells retract from one another along their junctions, leading to the interendothelial gaps. Cytokine induced response is somewhat delayed (4-6hrs) and long-lived(24hrs or more) in contrast to the histamine effect.

23. 3.DIRECT ENDOTHELIAL INJURY It results in endothelial cell necrosis and detachment. This effect is usually encountered in necrotizing injuries. It is due to direct damage to the endothelium by the injurious stimulus eg . Severe burns or lytic bacterial infections. Reaction is of TWO types- Immediate sustained response Delayed prolonged response

24. IMMEDIATE SUSTAINED RESPONSE Mostly, leakage starts immediately after injury & is sustained at higher level for several hours until the damaged vessels are thrombosed or repaired . All levels of the microcirculation are effected.including venules,capillaries and arterioles.

25. DELAYED PROLONGED LEAKAGE It is a common type of increased permeability that begins after a delay of 2 to 12 hours, lasts for several hours or even days. It involves venules as well as capillaries. Such leakage is caused by mild to moderate thermal injury,X -or ultraviolet irradiation & certain bacterial toxins -The late appearing sunburn is a good example of a delayed reaction It is attributable to apoptosis and the action of cytokines.

26. 4.LEUKOCYTE-DEPENDENT ENDOTHELIAL INJURY may occur as a result of leukocyte accumulation during the inflammatory response. Leukocytes adhere to the endothelium & may be activated in the process. Releasing toxic oxygen species and proteolytic enzymes Which then cause endothelial injury. Largely restricted to venules and pulmonary capillaries Late response Long lived

27. 5.INCREASED TRANSCYTOSIS Transcytosis occurs mainly through vesiculovacuolar organelle accross the intercellular junctions. venules Induced by histamine & most chemical mediators Certain factors eg.VEGF (vascular endothelial growth factor) causes vascular leakage by increasing the no. & size of these channels.

28. 6.Leakage from new blood vessels New vessel sprouts remain leaky during angiogenesis Certain factors eg.VEGF also increase vascular permeability. This causes edema which is the characteristic of early phase of healing. Although these mechanisms are seperable,they may all participate in response to any particular stimulus eg various stages of thermal burn Different chemical mediators may be produced in consecutive phases of the inflammatory response resulting in delayed or sustained vascular changes.

29. CELLULAR EVENTS It is divided into Leukocyte extravasation phagocytosis

30. EVENTS IN EXTRAVASATION OF LEUKOCYTES Margination & rolling Adhesion &transmigration across the endothelium(DIAPEDESIS) Migration in interstitial tissues toward a chemotactic stimulus

31. Margination & rolling In normal blood flow ,erythrocytes are confined to a central axial column displacing the leukocytes towards the wall of the vessel As vascular permeability increases in early inflammation, blood flow slows(stasis),hemodynamic conditions change & more white cells assume a peripheral position along the endothelial surface. This process of leukocyte accumulation is called MARGINATION

32. Subsequently,the leukocytes tumble slowly along the endothelium &adhere transiently(rolling). In time endothelium can be lined by white cells,an appearance called PAVEMENTING. ADHESIONS involved in rolling are accounted by selectin family of molecules

33. LEUKOCYTE ADHESION & TRANSMIGRATION Eventually leukocytes firmly adhere to the endothelial surface(adhesion) before crawling between the cells & through the basement membrane into the extravascular space( diapedesis ) It is regulated largely by the binding of complimentary adhesion molecules on the leukocytes & endothelial surfaces,& chemical mediators( chemoattractants & certain cytokines) modulate the surface expression of adhesion molecules.

34. The adhesion receptors involved belong to four molecular families- Selectins The immunoglobulin family Integrins Mucin -like glycoproteins

35. SELECTINS Characterized by N-terminal domain related to sugar-binding mammalian lectins,consists of- E- selectin (CD62E OR ELAM-1) P- selectin (CD62P or GMP140 or PADGEM) L- selectin (CD62L or LAM-1) E & P selectins bind through their lectin domains to sialyl -Lewis X oligosaccharide on certain glycoprotein on leukocytes.

36. IMMUNOGLOBULIN FAMILY IT INCLUDES- 2 endothelial adhesion molecules ICAM-1(intercellular adhesion molecule) VCAM-1(vascular cell adhesion molecule) Both serve as ligands for integrins found on leukocytes.

37. INTEGRINS Are transmembrane heterodimeric glycoproteins,made up of α and β chains. Are expressed on many cell types & bind to ligands on endothelial cells,other leukocytes & the extracellular matrix. Eg - β 2 integrins LFA-1 & Mac-1 bind to ICAM-1 β1 integrins VLA-4 bind VCAM-1

38. MUCIN LIKE GLYCOPROTEINS Such as haparan sulphate serve as ligand for the leukocyte adhesion molecule called CD44. These are found in the extracellular matrix and on cell surfaces.

39. Initial adhesion(rolling) is through selectins & glycosylated proteins. E &P selectins are upregulated at the inflammatory sites by specific mediators. L selectins on leukocytes bind CD34 glycoproteins on endothelial cells. Activation of leukocytes by selectin binding & mediators increases integrin avidity. Firm adhesion occurs via integrin endothelial cell receptor interaction.LFA-1 & Mac-1 integrins are on all leukocytes & bind to ICAM-1 on endothelial cells. Homotypic interaction of PECAM-1(CD31) on leukocytes & endothelial cells mediates transmigration between cells.( diapedesis ).

40. CHEMOTAXIS &ACTIVATION After extravasation,leukocytes emigrate towards the site of injury,along a chemical gradient in a process called chemotaxis . Both exogenous & endogenous substances can act as chemotactic agents for leukocytes. Most common exogenous agents are bacterial products eg -peptides that possess N- formyl - methionine terminal amino acid.

41. Endogenous chemoattractants include chemical mediators- Components of the complement system,C5a Products of the lipoxygenase pathway.leukotriene B 4 & cytokines(IL-8) Chemotactic agents bind to the specific receptors on the leukocyte cell surface & induce an intracellular cascade of phospholipid metabolites leading to increased intracellular calcium. Increased cytosolic calcium triggers the assembly of cytoskeketal contractile elements. Leukocytes move by extending pseudopods . The direction of movement is specified by a higher density of receptor- ligand interactions on one side of the cell. Locomotion involves assembling actin monomers into crosslinked polymers at the pseudopod’s leading edge.

42. Leukocyte activation Chemotactic factors also induce leukocyte activation Leukocytic activation result in- Production of AA metabolites. Degranulation & secretion of lysosomal enzymes & generation of oxidative bursts Modulation of leukocyte adhesion molecules including increased( or decreased) numbers & increased( or decreased) affinities.

43. PHAGOCYTOSIS Phagocytosis & release of lysosomal enzymes are the two major benefits from the accumulation of leukocytes at the site of inflammation. It consists of three main steps- Recognition & the attachment of the particle to the ingesting leukocyte Engulfment, with the subsequent formation of a phagocytic vaculoe Killing or degradation of the ingested material.

44. Recognition &attachment Neutrophils & macrophages can engulf the bacteria by recognition of the particles by the receptors expressed on the leukocyte surface. Mannose &scavenger receptors are the two important receptors that function to bind & ingest microbes. The efficiency of phagocytosis is greately enhanced when microbes are coated with serum proteins called opsonins ( opsonization ) for which the phagocytes express high affinity receptors.eg- IgG antibodies( Fc portion),the C3b breakdown product of complement (C3bi) & certain plasma lectins-MBL,all of which are recognized by specific receptors on leukocytes.

45. ENGULFMENT Binding of the opsonized particles triggers engulfment. Pseudopods are extended around the object to be engulfed forming a phagocytic vaculoe . The membrane of the vaculoe then fuses with the membrane of the lysosomal granule . Contents of the lysosomal granule are discharged into the phagolysosome resulting in degranulation of the leukocyte .

46. Killing & degradation Bacterial & microbial killing is accomplished largely by reactive oxygen species. Phagocytosis stimulates oxydative bursts characterized by a sudden increase in oxygen consumption, glycogen catabolism( glycogenolysis ) Increase glucose oxidation, Production of reactive oxygen metabolites. Oxygen metabolites are generated due to rapid activation of a leukocyte NADPH oxidase ,which oxidizes NADPH & in the process reduces O 2 to superoxide ion( O 2 - )

47. 2O 2 + NADPH 2O 2 - +NADP + +H + NADPH OXIDASE

48. Superoxide is then converted into hydrogen peroxide by dismutation . Lysosomes of neutrophils ( azurophilic granules ) contain the enzyme myeloperoxidase (MPO) & in the presence of halide such as Cl - ,MPO converts H 2 O 2 to HOCl - which is a powerful oxidant and antimicrobial agent that kills the bacteria by halogenation , protein & lipid peroxidation . Dead microorganisms are degraded by the action of lysosomal acid hydrolases . Other constituents of the leukocyte granules are capable of killing bacteria.these include lysosome,lactoferrin,bactericidal permeability increasing protein(BPI) & defensins .

49. PHAGOCYTOSIS

50. LEUCOCYTE- INDUCED TISSUE INJURY Activated leucocytes Reactive oxygen species and products of AA metabolism Direct endothelial injury and and tissue damage. Persistent activation of the leukocytes underlies many diseases in humans. Eg -Rheumatoid arthritis,chronic lung disease)

51. DEFECTS IN LEUCOCYTE FUNCTION Cause-genetic -acquired Vulnerability to infections Infections can be -recurrent & - life threatening

52. Three types 1. Defects in adhesion LAD-I ( Leucocyte Adhesion deficiency I) caused by defective synthesis of CD 18 subunit of leucocyte integrins LFA-1 and Mac-1

53. 2 . LAD -2 –caused by general defect of fucose metabolism Absence of sialyl -Lewis X(oligosaccharide epitope that binds E- and P- selectins )

54. 2. Defects in chemotaxis or phagocytosis Chediak Higashi syndrome caused by Disordered assembly of microtubules Results in Impaired locomotion & lysosomal degranulation into phagosomes

55. 3 . Defects in microbicidal activity Chronic granalumatous lung disease Genetic deficiency in a component of NADPH oxidase (generates superoxide) Engulfment of bacteria doesn’t result in oxygen dependent killing mechanism.

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