Acute inflammation- cellular events

Acute inflammation- cellular events


ACUTE INFLAMMATION- CELLULAR EVENTS

Cellular events consist of 2 process-

  1. Exudation of leucocytes
  2. Phagocytosis

Cellular events have following steps-

Exudation of leucocytes

1. Margination-

  • Due to slowing and stasis, there is loss of plasma by exudation and narrowing of plasma zone and is called as margination.
  • So, the neutrophils come close to the vessel walls called as pavementing.

2. Rolling & adhesion-

  • It is brought by
  • P selectin or CD 62
  • PECAM- 1 involved in leucocyte migration from endothelial surface.

3. Transmigration-

  • Neutrophils between endothelial cells & basement membrane crosses membrane by damaging it locally which collagenases & escape out in extravascular space.
  • Occurs mainly in post- capillary venules except in lungs (capillaries)
  • Cytokines activates leukocyte & endothelial cell to induce PECAM- 1 or CD 31.
  • Diapedesis- is transportation of leucocytes through endothelial gap.
  • PECAM- 1 is most important adhesion molecule for diapedesis.

4. Chemotaxis-

  • Leucocyte moving towards sites of infection or injury along a chemical gradient by a process called chemotaxis (unidirectional).

Agents can be- 

  1. LTB4
  2. IL8
  3. C5a & C3a

B. Phagocytosis-

  • It is the process of engulfment of solid particulate material by the cells & the cells are called as phagocytes.
  • Process was given by Metchnikoff.

2 main types of cells are-

  1.  PMN (microphages)
  2.  Monocytes & neutrophils (macrophages)

It involves 3 steps-

I. Recognition and attachment-

  • Begins with leukocyte receptors binding to the nucleous and these recptors are-
  1. Mannose receptors
  2. Scavanger receptors
  • Normal human cells are protected from phagocytosis due to presence f N- acetylgalactosamine or terminal sialic acid.
  • Opsonisation is when phagocytosis is enhanced as microorganisms are coated with specific proteins ie. Opsonins from the serum.

Main opsonins present are-

  1. IgG opsonin- naturally occurring antibody
  2. C3b opsonin
  3. Lectins 

II. Engulfment-

  • Opsonised microbes are ready to be engulfed by formation of cytoplasmic pseudopods.
  • Both phagocytosis & chemotaxis requires polymerization of actin filament.

III. Killing & degradation-

It takes place in 2 ways-

  1. Intracellular- 2 types
  2. Oxygen dependent
  3. Oxygen independent

ii) Extracellular 

Neutrophil extracellular traps (NETS)-

  • These are extracellular fibrillar network.
  • Provides high concentration of antimicrobial substances at sites of infection.
  • Extracellular traps contains proteins from azurophillic granules.
  • Also know as beneficial suicider
  • Involved in pathogenesis of infection, inflammatory and thrombotic disorder.

Exam Important

Transmigration- 

  • Occurs mainly in post- capillary venules except in lungs (capillaries)
  • Cytokines activates leukocyte & endothelial cell to induce PECAM- 1 or CD 31.
  • Diapedesis- is transportation of leucocytes through endothelial gap.
  • PECAM- 1 is most important adhesion molecule for diapedesis.

Chemotaxis-

  • Leucocyte moving towards sites of infection or injury along a chemical gradient by a process called chemotaxis (unidirectional).

Agents can be- 

  1. LTB4
  2. IL8
  3. C5a & C3a

Phagocytosis

  • Normal human cells are protected from phagocytosis due to presence f N- acetylgalactosamine or terminal sialic acid.
  • Opsonisation is when phagocytosis is enhanced as microorganisms are coated with specific proteins ie. Opsonins from the serum.

Main opsonins present are-

  1. IgG opsonin- naturally occurring antibody
  2. C3b opsonin
  3. Lectins

Engulfment-

  • Opsonised microbes are ready to be engulfed by formation of cytoplasmic pseudopods.
  • Both phagocytosis & chemotaxis requires polymerization of actin filament.
Don’t Forget to Solve all the previous Year Question asked on Acute inflammation- cellular events

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