Cellular events in acute inflammation

1. Cellular events in acute inflammation DrRamadas Nayak Prof & HOD Pathology Yenepoya Medical College Mangaluru

3. CELLULAR EVENTS LEUKOCYTE EXTRAVASATION PHAGOCYTOSIS

4. LEUKOCYTE EXTRAVASATION

5. LEUKOCYTE EXTRAVASATION • Journey of leukocytes from the vessel lumen to the interstitial tissue, called extravasation.

6. LEUKOCYTE EXTRAVASATION-STEPS Across the endothelium In the lumen In interstitial tissue Margination Transmigration Rolling Chemotaxis Pavementing Adhesion to endothelium

7. Normally erythrocytes - central axial column, & leukocytes toward vessel wall. Cell free zone

8. In the lumen Margination Rolling Pavementing Adhesion to endothelium

9. Rolling/Activation Adhesion Transmigration Margination Selectins Integrins/Ig superfamily PECAM-1, others WBC Activation Endothelial Activation Chemoattractants Stimulus Chemotaxis

10. Neutrophil Margination

11. Leukocyte Extravasation-steps Margination • Process of leukocyte accumulation is called margination

12. Neutrophil Margination

13. Leukocyte Extravasation-steps Cell free zone

14. Rolling/Activation Adhesion Transmigration • Leukocytes tumble along the endothelium & adhere transiently (a process called rolling) Selectins Integrins/Ig superfamily PECAM-1, others WBC Activation Endothelial Activation Chemoattractants Rolling Stimulus Chemotaxis

15. Leukocyte Extravasation-steps Rolling Cell free zone • Leukocytes tumble along the endothelium & adhere transiently (a process called rolling)

16. Adhesion Rolling/Activation Adhesion Transmigration Selectins Integrins/Igsuperfamily PECAM-1, others WBC Activation Endothelial Activation Chemoattractants • Adhere firmly (resembling pebbles over which a stream runs without disturbing them). • Endothelium lined by white cells -called pavementing Stimulus Chemotaxis

17. Rolling/Activation Adhesion Transmigration Across the endothelium Selectins Integrins/Igsuperfamily PECAM-1, others WBC Activation Endothelial Activation Chemoattractants Escape into the extravascular space -Transmigration across the endothelium (also called diapedesis) Stimulus Chemotaxis

18. Rolling/Activation Adhesion Transmigration Across the endothelium Selectins Integrins/Igsuperfamily PECAM-1, others WBC Activation Insert pseudopods into the junctions between the endothelial cells, squeeze through interendothelial junctions, & assume a position between the endothelium & basement membrane Endothelial Activation Chemoattractants Stimulus Chemotaxis

19. Leukocyte Extravasation-steps Across the endothelium Escape into the extravascular space -Transmigration across the endothelium (also called diapedesis) Insert pseudopods into the junctions between the endothelial cells Blood vessel Squeeze through interendothelial junctions Opening of gap between endothelial cells

20. Rolling/Activation Adhesion Transmigration In interstitial tissue Chemotaxis WBC Activation Endothelial Activation Chemoattractants Stimulus Chemotaxis Migration in interstitial tissues toward a chemotactic stimulus

21. Leukocyte Extravasation-steps In interstitial tissue -Chemotaxis After extravasation, leukocytes migrate in the interstitial tissues toward the site of injury by a process called chemotaxis Chemotaxis=Defined most simply as locomotion oriented along a chemical gradient Stimulus

22. Phagocytosis

23. Phagocytosis and Clearance of the Offending Agent • Many leukocytes recognize, internalize, and digest foreignmaterial, microorganisms, or cellular debris by a processtermed phagocytosis. It consists of three steps • Recognition and attachment • Engulfment • Killing or degradation of the ingested materia

25. Recognition and Attachment • Receptors on the surface of phagocytic cells recognizecomponents of microbes and necrotic cells.

26. Recognition and Attachment • Leukocytes express several receptors that recognize external stimuli. These include • (1) receptors for microbial products (e.g. Toll-like receptors-TLRs) • (2) G protein–coupled receptors (recognize N-formylmethionie residues) • (3) receptors for cytokines (for INF-γ) and • (4) receptors for opsonins

27. PhagocytosisRecognition and Attachment • One of the main receptors is mannose receptors. • Phagocytosis is enhanced when microbes are opsonized • Microbes gets attached to the receptor Mannose receptor Microbe Lysosomes Leukocytes

28. Recognition and Attachment • Receptors for opsonins (phagocytic receptor): • The phagocytosis is enhanced when leukocyte receptorsrecognize microbes coated by specific host proteinsknown as opsonins. • The major opsonins are • IgG antibodies • C3b breakdown product of complement,certain plasma lectins called collectins

29. Clinical signifcance of opsonins • After exposure to antigen, B cells get activated and matureinto plasma cells, which produces immunoglobulins (IgG). • Bruton disease: Defect in maturation of the B-cells leadingto absence of immunoglobulin production. Hence, there isdefective opsonization.

31. Phagocytosis Engulfment. • Next step in phagocytosis is engulfment and formation of a phagocytic vacuole. • Phagocyte membrane zips around microbe. Mannose receptor Microbe Lysosomes

32. Phagocytosis Engulfment. • Phagosome: Extensions of the cytoplasm of leukocyteform pseudopods surrounding the particle to be ingested and forms a vesicle or vacuole called a phagosome. Mannose receptor Microbe Lysosomes

33. Engulfment Microbe ingested in phagosome Phagosome with ingested microbe Lysosome with enzymes

34. Engulfment Phagolysosome Membrane of phagosome fuses with membrane of a lysosomal granule

35. Engulfment Discharge of the granule's contents into the phagolysosome

36. Engulfment • Phagolysosome: The membrane of phagosome fuseswith membrane of lysosome to form a phagolysosome.Lysosomal granules are discharged into this phagolysosome

37. Clinical significance of defects in phagolysosomefunction • Chédiak-Higashi syndrome: Autosomal recessive conditioncharacterized by: • Increased susceptibility to infections: Due to defectivefusion of phagosomes and lysosomes in phagocytes.

39. Killing and Degradation • Killing and degradation of ingested microbial agents/particles occurs within neutrophils and macrophages. • Most important microbicidal agents are: • (1) reactive oxygen species • (2) reactive nitrogen species-derived from nitric oxide (NO) • (3) lysosomal enzymes.

40. Killing and Degradation • Reactive oxygen species (ROS): • Types of ROS are:

41. Reactive oxygen species (ROS) • Mechanism of production • In the phagocytic vacuole of leukocyte, rapid activation of NADPH oxidase (also called phagocyte oxidase), oxidizes NADPH (reduced nicotinamide-adenine dinucleotide phosphate) to NADP.

42. Reactive oxygen species (ROS): • Amount of H2O2 is insufficient to kill most of themicrobes by itself but the enzyme myeloperoxidase(MPO) present in the azurophilic granules of neutrophils can convert it into a powerful ROS. • MPO in the presence of a halide such as Cl–, converts H2O2 to hypochlorousradical (HOCl•), which is a potent oxidantand antimicrobial agent. • Hypochlorite (HOCl•) destroys microbes either by halogenation or by proteins and lipid peroxidation. • H2O2is also converted to hydroxyl radical (•OH) whichis also powerful destructive agent.

43. Reactive nitrogen species • NO, which is generated from arginine by the action of nitricoxide synthase (NOS), can kill microbes similar to ROS. • NO reacts with superoxide and produces highlyreactive free radical peroxynitrite (ONOO•).

44. Lysosomal enzymes • Acid hydrolases of lysosomes degrade the dead microorganisms. • Elastasecan kill bacteria.

45. Lysosomal enzymes • Constituents of leukocyte granules: The microbicidalsubstances within leukocyte cytoplasmic granulesinclude: • Bactericidal permeability—increasing protein • Lysozyme and lactoferrin • Major basic protein (MBP) present in eosinophils iscytotoxic to many parasites • Defensinsare toxic to microbes • Cathelicidins: These are antimicrobial proteins in theneutrophils and other cells. They are very effectiveagainst Mycobacterium tuberculosis

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