Does IgE bind to and activate eosinophils from patients with allergy?

Area of Science:

• Immunology
• Allergy Research
• Cell Biology

Background:

• Eosinophils are implicated in allergic diseases, with prior reports suggesting expression of the high-affinity IgE receptor (FcεRI).
• The precise surface expression level and functional relevance of FcεRI on human eosinophils remain unclear.
• Investigating FcεRI's role is crucial for understanding eosinophil-mediated allergic responses.

Purpose of the Study:

• To quantify FcεRI surface expression on human eosinophils.
• To determine if FcεRI engagement triggers eosinophil effector functions.
• To compare the role of IgE receptors versus IgG receptors in eosinophil activation.

Main Methods:

• Flow cytometry (FACS) analysis of blood eosinophils from allergic patients.
• In vitro sensitization with chimeric IgE (cIgE) followed by detection.
• Stimulation assays using IgE, anti-IgE, IgG, and anti-IgG to assess mediator release (leukotriene C4, superoxide) and degranulation.

Main Results:

• Standard FACS detected FcγRII (CD32) but not FcεRI on eosinophils.
• Sensitive detection revealed minimal FcεRI expression, approximately 0.5% of basophil levels.
• Eosinophils failed to degranulate or release mediators upon IgE or anti-IgE stimulation.
• Eosinophils exhibited functional responses to IgG stimulation.

Conclusions:

• Human eosinophils express very low levels of FcεRI, insufficient for significant effector functions in allergic conditions.
• FcγRII and IgG appear to play a more prominent role in eosinophil activation than FcεRI.
• These findings suggest alternative pathways, potentially involving IgG or cytokines like IL-5, are key in eosinophil-driven allergic inflammation.