What are eosinophils associated with?

Eosinophil Associations in Health and Disease

Eosinophils are primarily associated with allergic disorders, parasitic infections, and various inflammatory conditions that can affect multiple organ systems. 1

Primary Associations of Eosinophilia

• Allergic disorders account for approximately 80% of cases of eosinophilia, including asthma, food allergies, and atopic dermatitis 1
• Parasitic infections, particularly intestinal helminths, are the second most common cause of eosinophilia 1
• Eosinophilic esophagitis (EoE) is characterized by esophageal dysfunction and mucosal biopsy specimens containing ≥15 eosinophils per high-power field 2
• Hypereosinophilic syndromes (HES) are characterized by elevated eosinophils in peripheral blood (>1500 cells/μL) and organ damage due to eosinophilic infiltration 2
• Drug hypersensitivity reactions, particularly to NSAIDs, beta-lactam antibiotics, and nitrofurantoin 1
• Autoimmune diseases including eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss syndrome) 2
• Hematological and solid neoplasias can be associated with eosinophilia 1

Organ-Specific Eosinophilic Disorders

Gastrointestinal System

• Eosinophilic esophagitis (EoE) presents with symptoms of esophageal dysfunction (dysphagia, food impaction in adults; feeding problems, vomiting in children) 2
• EoE is characterized by ≥15 eosinophils per high-power field in esophageal biopsies and is often associated with other atopic conditions 2
• Eosinophilic microabscesses, surface layering of eosinophils, basal layer hyperplasia, and lamina propria fibrosis are additional histopathological features of EoE 2
• 50-80% of EoE patients have concurrent atopic conditions (allergic rhinitis, asthma, eczema) 2
• Eosinophilic gastroenteritis can involve any part of the GI tract and may be associated with peripheral eosinophilia 2

Respiratory System

• Eosinophils are key players in allergic rhinitis, where they contribute to nasal mucosal inflammation 2
• In asthma, eosinophils contribute to airway inflammation and remodeling 1
• Nasal eosinophilia correlates with severity of perennial allergic rhinitis in children 2
• Intranasal corticosteroids like fluticasone propionate decrease nasal mucosal eosinophils in 66% of patients with allergic rhinitis 3

Systemic Manifestations

• Hypereosinophilic syndromes (HES) can affect multiple organs including the gastrointestinal tract, heart, skin, lungs, and nervous system 2
• Up to 38% of HES patients have gastrointestinal symptoms 2
• Persistent high-grade eosinophilia (>1.5 × 10⁹/L) can cause significant organ damage even without an identifiable cause 1
• Eosinophilic granulomatosis with polyangiitis (EGPA) follows a three-stage pattern: prodromal (allergic rhinitis, asthma), eosinophilic (blood and tissue eosinophilia), and vasculitic (affecting multiple organ systems) 2

Immunological Role of Eosinophils

• Eosinophils are associated with Th2 immune responses and produce cytokines including IL-4, IL-5, and IL-13 2
• They contain cytotoxic granule proteins (eosinophil cationic protein, eosinophil-derived neurotoxin, peroxidase, major basic protein) that can damage tissues 2
• Eosinophils can function as antigen-presenting cells and modulate T cell responses 4
• They play a role in immune homeostasis and can suppress over-reactive pro-inflammatory responses 4
• Eosinophils interact with microbiota, though the exact nature of this relationship is still being investigated 4

Diagnostic Considerations

• Peripheral eosinophil counts are elevated in 10-50% of adults and 20-100% of children with eosinophilic esophagitis, though usually only modestly (2-fold) 2
• Nasal smears for eosinophils can help diagnose allergic rhinitis and nonallergic rhinitis with eosinophilia 2
• The absence of eosinophils with large numbers of neutrophils suggests infectious rhinitis or sinusitis 2
• A detailed history of travel, exposures, medications, and symptoms is essential for evaluating eosinophilia 1

Treatment Approaches

• Topical glucocorticosteroids are effective in reducing esophageal eosinophil counts in EoE 2
• Dietary elimination strategies are effective in EoE, with moderate certainty for elemental diets 2
• Proton pump inhibitors may be effective in some patients with esophageal eosinophilia 2
• Dupilumab, a monoclonal antibody to IL-4 receptor alpha, is FDA-approved for EoE 2
• Intranasal corticosteroids like fluticasone propionate decrease nasal mucosal eosinophils in allergic rhinitis 3

Clinical Pearls and Pitfalls

• Eosinophilia can be transient during the tissue migration phase of parasitic infections, when microscopic studies may be negative 1
• Serological tests for helminths may not become positive until 4-12 weeks after infection and may exhibit cross-reactivity 1
• Seasonal variations in symptoms and esophageal eosinophil levels have been reported in EoE patients 2
• HES can often be distinguished from EoE by the presence of peripheral eosinophilia (>1500 cells/μL), which is rare in isolated EoE 2
• The nasal eosinophil count correlates with the severity of perennial allergic rhinitis and may predict the progression to asthma 2