eosinophil

Function

• eosinophils are involved in allergic responses & are the 1st line of defense against helminths
• eosinophils are phagocytes
  • phagocytosis of foreign particles
  • phagocytosis of antigen-antibody complexes
• eosinophic granules contain inflammatory mediators
  • larger granules
    • major basic protein
    • acid hydrolases
    • eosinophil peroxidase
    • phospholipase
    • eosinophil cationic protein (ribonuclease-3)
    • eosinophil-derived neurotoxin (ribonuclease-2)
    • eosinophil protein X
  • smaller granules
    • arylsulfatase
    • acid phosphatase
• eosinophils also produce:
  • reactive oxygen species
  • LTC4
  • platelet-activating factor
  • cytokines
• eosinophils dampen inflammatory responses

Pathology

• Charcot-Leyden crystals (a product of eosinophil degeneration) may be seen in areas of eosinophil accumulation
• inflammatory mediators of eosinophils are toxic to respiratory epithelial cells & result in shedding of these cells
• Creola bodies are clumps of sloughed respiratory epithelium in sputum of asthmatic patients

Biochemistry

• eosinophils express the chemokine receptor CCR3

Physiology

• derived from common granulocyte-monocyte stem cell in bone marrow -> committed eosinophilic progenitor cell
• 3 growth factors produced by lymphocytes affect eosinophil maturation (GM-CSF, IL2 & IL5)
• IL5 promotes terminal maturation & functional activation & prevents apoptosis of eosinophils
• 1/2 life in peripheral blood is ~ 18 hours after which they migrate into tissues where they survive for at least 6 days
• adrenocortical steroids expedite eosinophil migration from blood into tissues
• neutrophils in tissues are ~100 X more abundant than in blood
• within tissues they are found at epithelial barriers to the outside word, i.e. lung & respiratory tract, GI tract, skin
• eosinophil chemotactic factors:
  • leukotrienes
  • platelet-activating factor (PAF)
  • cytokines:
    • interleukin-5 (IL-5)
    • monocyte chemotactic protein
    • RANTES
• other factors in eosinophil recruitment
  • induction of VCAM-1 by endothelial cells b ) VCAM-1 binding of VLA-4 on eosinophils

Laboratory

• component of complete blood count with differential
• normal eosinophil count is 150-300/uL, & 1-4% of circulating WBC
• see ARUP consult

More general terms

• granulocyte

Additional terms

• eosinophil peroxidase (EPX, EPER, EPO, EPP)
• eosinophilia
• eosinophilia-myalgia syndrome (EMS)
• eosinophilic esophagitis
• eosinophilic fasciitis (Shulman's syndrome)
• eosinophilic folliculitis
• eosinophilic gastroenteritis
• eosinophilic granuloma
• eosinophilic leukemia
• eosinophilic pneumonia; Andrews syndrome; pulmonary eosinophilia
• eosinophils in blood
• eosinophils in urine
• eosinophiluria