eosinophils and mast cells

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eosinophils and mast cells
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eosinophil
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Eosinophil introduction

• bone marrow derived granulocytes
• Myeloid lineage
• Paul Ehrlich 1879 red, eosinophilic basic
  granules
• nucleus divided into two tear-shaped lobes
• non-dividing - approx 13 hr in circulation
• usually less than 4 of WBC
• secretory function

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Eosinophil function

• increase (eosinophilia) associated with
• parasite infections eg. helminths
• allergy eg. Aspergillus fumigatus
• some poorly understood immunological conditions
  eg. Churg-Strauss syndrome, Loefflers syndrome,
  endomyocardial fibrosis
• increase in - blood, bronchial tissue, skin,
  nasal polyps and gut tissue

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Eosinophil IL-5

• IL-5 eosinophil recruitment, proliferation,
  maturation, maintenance and activation factor
• Bone marrow cultures with IL-3 and GM-CSF
  produce very few eosinophil colonies. T-cell
  derived IL-5 is required.
• IL-5 is a heterogeneous glycoprotein 32 - 62kDa.
  Gene on the long arm of chromosome 5, along with
  the other haematopoetic growth factors GM-CSF,
  IL-3, IL-4.
• IL-5 enhances phagocytic activity, stimulates
  superoxide production, upregulates IgG and IgE Fc
  and complement receptors, delays apoptosis -
  prolongs eosinophil survival
• Humanised monoclonal anti-IL-5 decreases
  circulating eosinophils

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Eosinophil selective traffic

• Eosinophils need to move to sites of inflammation
  and adhere to and
• cross pulmonary vascular epithelial cells. This
  involves
• Eosinophil chemotactic factors
• eosinophil chemotactic factor of anaphylaxis
  (ECF-A) from mast cells
• Val-Gly-Ser-Glu and Ala-Gly-Ser-Glu
• N-formyl peptides (f-Met-Leu-Phe) bacteria
• C5a complement activation
• ecalectin T cell derived, 36-kDa protein
• eotaxin CCR3 chemokine from lung and skin
  stromal cells
• MIP-1, RANTES, MCP-3 monos,T cells, platelets,
  basophils

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eotaxin

• CCR-3 receptor-specific, eosinophil-selective
  chemokine.
• 8.4 kDa, 74 amino acid polypeptide
• mast cell and macrophage-produced TNF-a and IL-1a
  act on adjacent epithelium, endothelium,
  lymphocytes, macrophages and eosinophils to
  produce eotaxin.
• receptor is a 355 aa residue seven transmembrane
  domain, G-linked protein exclusively on
  eosinophils.
• is unique among known C-C chemokines in that it
  binds to only one receptor, CCR-3 (Kd0.1-1.5
  nM).
• has no known activity on neutrophils, macs or
  lymphocytes.
• induces the production of ROS
• synergises with IL-5
• eosinophils also produce IL-4, IL-5 and Eotaxin

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Eosinophil selective traffic

• Adhesion
• the alpha-4 integrin (very late activation
  antigen) VLA-4 on eosinophils binds to the
  adhesion molecule VCAM-1 on vascular endothelium.
• Transmigration
• the beta-2 integrin p-selectin on eosinophils
  binds to its ligand ICAM-1 on vascular endothelium

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eosinophil life cycle
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Eosinophil receptors and degranulation

• CD4, HLA-DR, CD25, IL-5R, CCR3R etc.
• CD23, low affinity IgE receptor Fc epsilon R11 -
  selective for EPO, MBP but not ECP.
• CD32, high affinity IgG receptor Fc gamma R11 -
  selective for ECP not EPO.
• CD35, type 1 high-affinity complement receptor
  CR1 binds C3b / C3d and C4b.
• synergy with IL-3, IL-5, GM-CSF, TNF, IFN-beta,
  PAF.

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Eosinophil mediators

• Preformed
• stored in cytoplasmic granules
• Produced on activation
• lipid mediators
• cytokines

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Eosinophil preformed mediators

• The cytoplasmic granules are membrane bound and
  contain a
• crystalloid protein core. The granule and cell
  membranes fuse
• on triggering and release the granule contents.
• The granules contain four highly toxic
  arginine-rich proteins
• with a high isoelectric point pH gt 11.0
• major basic protein (MBP),
• eosinophil cationic protein (ECP),
• eosinophil peroxidase (EPO),
• eosinophil-derived neurotoxin (EDN).
• These bind the negatively charged surfaces of
  parasites.

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Eosinophil basic proteins 1

• ECP 21 kDa
• kills certain parasites
• potent neurotoxin
• induce histamine release from mast cells
• down-regulate T-cell proliferation
• shortens clotting time
• alters the GAG production by fibroblasts
• Controlled by binding of heparin and -2
  macroglobulin.
• EDN 18kDa (70 homology with ECP)
• kills parasites
• potent neurotoxin
• potent ribonuclease

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Eosinophil basic proteins 2

• EPO 74 kDa
• peroxidase activity - ie. generation of cytotoxic
  free radicals
• degranulates mast cells
• platelet aggregation
• Controlled by uptake and neutralisation by
  neutrophils
• MBP 14 kDa
• Toxic to certain parasites, tumour cells and
  mammalian cells
• degranulates mast cells
• neutralises heparin
• platelet aggregation
• cytotoxic for bronchial epithelium - leading to
  airways hyper-reactivity.

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Eosinophil newly synthesised mediators

• Lipids
• Leukotrienes LTC4, D4, E4. These prolong
  broncho-constriction, mucus secretion, increased
  vascular permeability.
• Cytokines
• IL-3, IL-5, IL-13, GM-CSF. Content increased in
  allergic patients
• Reactive oxygen metabolites
• oxidative burst
• Regulatory enzymes
• histaminase histamine
• phospholipase PAF
• arysulphatase B leukotrienes
• collagenases basement membrane

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Eosinophil protective role against parasites

• Eosinophils kill the schistosomula (egg) stage of
  Schistosoma mansoni
• Degree of protection against nematodes in guinea
  pigs and sheep correlates with eosinophilia.
• Genetic determination - strain-dependent
  differences in eosinophilia following parasitic
  infection in mice. Possibly related to IL-5 or
  eotaxin polymorphism.
• Mice infected with Trichonella spiralis treated
  with anti-eosinophil antibody cannot eliminate
  the worms and have more muscle cysts.

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Eosinophil pathogenic role in allergy

• Eosinophils abundant in allergic sites
• ECP / MBP cause damage and denudation of
  bronchial epithelium, and can cause impairment of
  ciliary beating. Seen in biopsy of asthma
• Serum and bronchial lavage / sputum ECP levels
  raised in
• asthmatics
• seasonal hay fever
• experimental asthma challenge
• IL-5 KO mice lack bronchial hyper-reactivity.

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Eosinophil resolution of inflammation

• Apoptosis - eosinophils retain granules but lose
  the ability to secrete them. Apoptotic
  eosinophils are ingested and digested by
  macrophages in a non-inflammatory process.
• Steroid treatment - very effective for
  eosinophil-mediated diseases.
• prevents transcription of eosinophil cytokines
• accelerates eosinophil apoptosis
• downregulates VCAM-1

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eosinophil summary

• recruited from bone marrow
• chemotaxis, attachment and diapedesis
• functions with other factors / cells
• non-specific recognition
• secretion of toxic mediators
• effective against extra-cellular parasites
• resolution of inflammation