Human eosinophils in vitro. An ultrastructural morphology primer

Area of Science:

• Cell Biology
• Hematology
• Immunology

Background:

• Human eosinophils exhibit diverse ultrastructural morphologies influenced by their in vivo state (e.g., mature, immature, activated).
• These in vivo morphological changes are largely recapitulated in in vitro culture systems.

Purpose of the Study:

• To provide an ultrastructural morphological primer of human eosinophils, covering their various forms in vivo and in vitro.
• To correlate observed morphologies with cellular processes like differentiation, maturation, activation, secretion, and injury.

Main Methods:

• Examination of mature and immature eosinophils from peripheral blood and bone marrow.
• Analysis of activated tissue eosinophils.
• Review of published studies on in vitro eosinophil culture systems supplemented with growth factors (IL-5, IL-3) and c-kit ligand.
• Observation of eosinophil peroxidase (EPO) release via piecemeal degranulation (PMD).

Main Results:

• In vivo and in vitro eosinophil morphologies reflect differentiation, maturation, activation, secretion, and cell injury.
• Human IL-3 and IL-5 demonstrate eosinophil-promoting, -sustaining, and -activating properties.
• Eosinophils release EPO via piecemeal degranulation (PMD), a process involving transport in cytoplasmic vesicles without granule fusion.
• C-kit ligand-supplemented cultures of human cord blood show diverse eosinophil subcellular changes mirroring in vivo processes.

Conclusions:

• The diverse ultrastructural changes observed in human eosinophils, both in vivo and in vitro, are indicative of key cellular processes.
• This primer aids researchers in identifying eosinophils within complex cell cultures containing other hematopoietic lineages.
• Understanding eosinophil morphology is crucial for interpreting their function and response to stimuli in various biological contexts.