Eosinophils (Eo)

Eosinophils (Eo)

Definition: Eosinophils (Eo) are a type of white blood cell (WBC) that plays a crucial role in the immune system, particularly in combating parasitic infections and mediating allergic reactions. They are characterized by their bilobed nucleus and large granules that stain bright red with eosin dye.

Characteristics of Eosinophils

• Morphology: Eosinophils have a distinctive bilobed nucleus and contain granules filled with enzymes and toxic proteins.
• Lifespan: They typically circulate in the bloodstream for a few hours and can reside in tissues for several days.

Functions of Eosinophils

• Defense Against Parasites:

• Eosinophils are particularly effective against larger parasites, such as helminths (worms). They release cytotoxic granules containing proteins like major basic protein (MBP) and eosinophil peroxidase that damage the parasite’s cell membrane.

• Allergic Reactions:

• Eosinophils play a significant role in allergic responses, such as asthma and hay fever. They are recruited to sites of inflammation where they release inflammatory mediators, contributing to tissue damage and symptoms associated with allergies.

• Regulation of Inflammation:

• Eosinophils secrete various cytokines and chemokines that can modulate the activity of other immune cells, influencing the overall inflammatory response.

• Tissue Repair:

• They can contribute to tissue remodeling and repair following inflammation, although their activity can also lead to chronic inflammation and diseases if dysregulated.

Activation of Eosinophils

• Chemotaxis: Eosinophils are attracted to sites of infection or inflammation by chemokines released from damaged tissues or other immune cells.
• Receptor Engagement: Activation occurs through various receptors that recognize specific stimuli, including IgE antibodies bound to allergens.

Clinical Relevance

• Eosinophilia: An elevated eosinophil count can indicate various conditions, including allergic diseases, parasitic infections, and certain hematological disorders.
• Asthma and Allergies: Eosinophils are often found in increased numbers in the airways of asthma patients, contributing to airway inflammation and hyperreactivity.
• Eosinophilic Disorders: Conditions characterized by excessive eosinophil activation or accumulation can lead to tissue damage, such as eosinophilic esophagitis or hypereosinophilia.

Conclusion

Eosinophils are vital components of the immune system with specialized roles in fighting parasites and mediating allergic responses. Understanding their functions and mechanisms is crucial for diagnosing and treating various allergic conditions, infections, and inflammatory diseases.

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References

1. Rothenberg ME, et al. “Eosinophilia.” New England Journal of Medicine. 2006; 354(24): 2599-2610. DOI: 10.1056/NEJMra051872
2. Weller PF, et al. “Eosinophils: Biology and Role in Health and Disease.” Nature Reviews Immunology. 2006; 6(11): 974-985. DOI: 10.1038/nri1985
3. Dyer KD, et al. “Eosinophils in Health and Disease.” Journal of Allergy and Clinical Immunology. 2013; 132(4): 844-854. DOI: 10.1016/j.jaci.2013.09.019