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Extravasation
                    Neutrophils
   Active phagocytic cells like macrophages
   Primary and secondary granules containing lytic
    enzymes and bactericidal substances
   Primary granules
     • larger, denser, contain peroxidase, lysozyme and
       various hydrolytic enzymes
   Secondary granules
     • smaller, contain collagenase, lactoferrin,
       lysozyme
   Granules fuse with phagosomes and cause
    digestion
                     Neutrophils
   Kill ingested microorganisms
    • Antimicrobial substances (oxygen-dependent
      and oxygen-independent pathways)
          Larger respiratory burst
          more reactive oxygen intemediates
          reactive nitrogen intermediates
          higher expression of defensins
Neutrophils
                  Eosinophils
   Nucleus is bilobed
   Cytoplasmic granules stain with acid dye:
    Eosin Red
   Motile (from blood to tissues), phagocytic
    cells
   A more important role is against parasites
   Eosinophilic granules secrete contents that
    damage the parasite membrane
Eosinophils
                   Basophils
   Lobed nucleus
   Heavily granulated
   Granules stain with basic dye: methylene
    blue
   Nonphagocytic granulocytes
   Substances present in their cytoplasmic
    granules usually cause allergies
Basophils
                     Mast cells
   Formed in bone marrow and released as un-
    differentiated cells
   Differentiate after arrival in tissues like skin,
    connective tissue in different organs,
    mucosal epithelial tissue of respiratory,
    digestive and genito-urinary tracts
   Large number of cytoplasmic granules
    containing histamine and other substances
   Role in the development of allergies
                    Dendritic cells

   Long membrane extensions resembling dendrites of
    nerve cells
   Major function: presentation of antigen to Th cells
   Common function of all types of dendritic cells:
    -Display of class I and II MHC molecules, B7 family of
    costimulatory molecules, CD80 and CD86, CD40
    -Capture antigen in one location and present it in
    another location
Dendritic cells-Antigen Presentation
Dendritic cells-Antigen Presentation
                 Dendritic cells
   Immature cells monitor pathogenic invasion and
    capture the invading antigen by
     • Phagocytosis or internalization by receptor
       mediated endocytosis or imbibation by
       pinocytosis (about 1000 to 1500µm3 fluid/hr)
   Migration to lymph nodes
   Maturation starts with loss of capturing functions
    and increased expression of MHC-II and
    costimulatory molecules for presentation
   Presentation of antigen to T cells
                     Dendritic cells
   Four types:
    • Langerhans cells (epidermis)
    • Interstitial dendritic cells (interstitial spaces of all
      organs except brain)
    • Monocyte-derived dendritic cells (arise from
      blood monocytes after their migration into
      tissues, then move to lymph nodes or back to
      blood
    • Plasmacytoid-derived dendritic cells
          Arise from plasmacytoid cells
          Play roles in innate immune defense and as antigen
           presenting cells
         Mononuclear phagocytes
   Monocytes in circulation and macrophages in
    tissues
   Pro-monocytes develop from granulocyte-
    monocyte progenitor cells and leave bone
    marrow to enter blood and differentiate into
    mature monocytes
   Within 8hr, monocytes enlarge and enter
    tissues to become macrophages
    • Tissue macrophages
    • Free or wandering macrophages
                   Macrophage
   Changes during differentiation of a monocyte
    to macrophage:
    • 5 to 10 fold enlargement of cell size
    • Increase in number & complexity of intracellular
      organelles
    • Increased phagocytic ability
    • Increased production of hydrolytic enzymes
    • Secretion of different soluble factors
             Activated macrophages
   Activation takes place by:
    • Phagocytosis of particulate antigen
    • Contact with receptors that sense microbial
      pathogens
    • Cytokines secreted by Th cells
    • Inflammatory mediators
   After activation:
    • Greater phagocytic activity, increased ability to kill
      ingested microbes, increased production of
      inflammatory mediators, increased ability to
      activate Th cells by increased MHC-II expression
                 Phagocytosis
   Adherence of antigen induces pseudopodia
    (membrane protrusions) to extend around the
    attached material
   Fusion of pseudopodia encloses the material
    within a membrane bound structure
    (phagosome)
   Phagosome enters endocytic processing
    pathway
   Movement towards interior of the cell, fusion
    with the lysosome (phagolysosome)
   Digestion with hydrolytic enzymes
Summary

				
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