ACTIVE RECALL 1

• Percentage in Bone Marrow

  1% to 3% of nucleated cells
• Composition of Bone Marrow

  • Mature eosinophils (slightly more than a third)
  • Eosinophilic metamyelocytes (a quarter)
  • Eosinophilic promyelocytes/myelocytes (remainder)
• Percentage in Peripheral Blood

  1% to 3% of leukocytes
• Absolute Number

  Up to 0.4 × 10^9/L
• Eosinophil Development Origin


  Arise from the common myeloid progenitor (CMP)
• Cytokines Involved in Eosinophil Development

  • IL-3
  • IL-5
  • GM-CSF
• IL-5


  Crucial for eosinophil growth and survival
• Transcription Factors

  • GATA-1
  • PU.1
  • c/EBP
• Eosinophilic Promyelocytes (Stage 1)


  Identified cytochemically by Charcot-Leyden crystal protein in primary granules
• Early Myelocytes (Stage 2)


  First stage identifiable as eosinophilic using light microscopy and Romanowsky staining
• Eosinophil Myelocytes (Stage 3)


  Secondary Granules: Large, pale reddish-orange granules visible at the light microscope level<|>Primary Granules: Azure granules in blue cytoplasm<|>Nucleus: Similar to neutrophil myelocytes
• Eosinophil Metamyelocytes and Bands (Stage 4)


  Nuclear Shape: Resemble neutrophil counterparts (+ kidney bean shape)<|>Granules: 2nd: Increase in number; formation of third type secretory granule or secretory vesicle<|>Organelles: Lipid bodies and small granules present
• Mature Eosinophils (Last stage -> ready for release)


  Nucleus: Typically bilobed<|>Cytoplasm: Contains characteristic refractile, orange-red secondary granules<|>Extensive secretory vesicles, which increase considerably when stimulated or activated
• Eosinophil Development Duration


  From the last myelocyte mitotic division to the emergence of mature eosinophils from the marrow takes about 3.5 days
• Turnover Rate

  Approximately 2.2 × 10^8 cells/kg per day
• Storage Pool


  A large storage pool in the marrow consisting of between 9 and 14 × 10^8 cells/kg
• Half-Life in Circulation

  Roughly 18 hours<|>The half-life is extended during conditions of eosinophilia
• Normal Tissue Destinations

  • Respiratory Tract
  • Gastrointestinal Tract
  • Genitourinary Tract
• Eosinophil Survival Time

  Variable (2-5 days)<|>Influenced by the presence of eosinophilia and the specific tissue environment they migrate to
• Primary Function of Eosinophils

  Play roles in immune regulation and response to infections, especially parasitic infections and allergic reactions
• Eosinophil Granule Contents


  Cytokines, chemokines, growth factors, and cationic proteins (previously synthesized proteins)
• Classical Exocytosis

  1. Granules move to the plasma membrane

  2. Fuse with the plasma membrane

  3. Empty contents into the extracellular space
• Compound Exocytosis

  1. Granules fuse together within the eosinophil

  2. The fused granule then fuses with the plasma membrane to release contents
• Piecemeal Degranulation

  1. Secretory vesicles remove specific proteins from secondary granules

  2. Vesicles migrate to the plasma membrane

  3. Fuse with the membrane to empty specific proteins into the extracellular space
• Eosinophils in Thymus Function

  Eosinophils transmigrate into the thymus of the newborn<|>Involved in the deletion of double-positive thymocytes
• Eosinophils as Antigen-Presenting Cells


  Promote the proliferation of effector T cells<|>Initiate type 1 or type 2 immune responses by rapidly secreting preformed cytokines in a stimulus-specific manner
• Eosinophils in Mast Cell Regulation

  Release major basic protein (MBP), causing mast cell degranulation and cytokine production<|>Produce nerve growth factor, promoting mast cell survival and activation
• Eosinophils in Response to Parasitic Infections

  Eosinophil production increases during helminth infections<|>Capable of destroying tissue-invading helminths by: Secreting major basic protein and eosinophil cationic protein, Producing reactive oxygen species<|>Suggestion of a role in preventing reinfection
• Eosinophils in Asthma

  Eosinophil count in blood and sputum correlates with disease severity<|>Contributes to airway inflammation and mucosal cell damage through: Secretion/production of basic proteins, lipid mediators, reactive oxygen species, and cytokines like IL-5<|>Involved in airway remodeling via eosinophil-derived fibrogenic growth factors<|>Anti-IL-5 monoclonal antibody treatment can reduce exacerbations in certain asthmatic patients
• Eosinophils in Gastrointestinal Allergies

  Eosinophil accumulation occurs in disorders like food allergies, allergic colitis, and inflammatory bowel diseases (Crohn's disease and ulcerative colitis)