Eosinophilic mucus diseases.

Eosinophilic inflammation is primarily characterized by type 2 immune responses against parasitic organisms. In the contemporary human being especially in developed countries, eosinophilic inflammation is strongly associated with allergic/sterile inflammation, and constitutes an undesired immune reaction. This situation is in stark contrast to neutrophilic inflammation, which is indispensable for the host defense against bacterial infections. Among eosinophilic inflammatory disorders, massive accumulation of eosinophils within mucus is observed in certain cases, and is often linked to the distinctive clinical finding of mucus with high viscosity. Eosinophilic mucus is found in a variety of diseases, including chronic allergic keratoconjunctivitis, chronic rhinosinusitis encompassing allergic fungal sinusitis, eosinophilic otitis media, eosinophilic sialodochitis, allergic bronchopulmonary aspergillosis/mycosis, eosinophilic plastic bronchitis, and eosinophilic asthma. In these pathological conditions, chronic inflammation and tissue remodeling coupled with irreversible organ damage due to persistent adhesion of toxic substances and luminal obstruction may impose a significant burden on the body. Eosinophils aggregate in the hyperconcentrated mucus together with cell-derived crystals, macromolecules, and polymers, thereby affecting the biophysical properties of the mucus. This review focuses on the clinically significant challenges of mucus and discusses the consequences of activated eosinophils on the mucosal surface that impact mucus and persistent inflammation.

Aggregated eosinophils and neutrophils characterize the properties of mucus in chronic rhinosinusitis.

BACKGROUND: Airway obstruction caused by viscous mucus is an important pathophysiologic characteristic of persistent inflammation, which can result in organ damage. OBJECTIVE: We investigated the hypothesis that the biophysical characteristics of accumulating granulocytes affect the clinical properties of mucus. METHODS: Surgically acquired nasal mucus samples from patients with eosinophilic chronic rhinosinusitis and neutrophil-dominant, noneosinophilic chronic rhinosinusitis were evaluated in terms of computed tomography density, viscosity, water content, wettability, and protein composition. Isolated human eosinophils and neutrophils were stimulated to induce the formation of extracellular traps, followed by the formation of aggregates. The biophysical properties of the aggregated cells were also examined. RESULTS: Mucus from patients with eosinophilic chronic rhinosinusitis had significantly higher computed tomography density, viscosity, dry weight, and hydrophobicity compared to mucus from patients with noneosinophilic chronic rhinosinusitis. The levels of eosinophil-specific proteins in mucus correlated with its physical properties. Eosinophil and neutrophil aggregates showed physical and pathologic characteristics resembling those of mucus. Cotreatment with deoxyribonuclease and heparin, which slenderizes the structure of eosinophil extracellular traps, efficiently induced reductions in the viscosity and hydrophobicity of both eosinophil aggregates and eosinophilic mucus. CONCLUSIONS: The present study elucidated the pathogenesis of mucus stasis in infiltrated granulocyte aggregates from a novel perspective. These findings may contribute to the development of treatment strategies for eosinophilic airway diseases.

Galectin-10 as a Potential Biomarker for Eosinophilic Diseases.

Galectin-10 is a member of the lectin family and one of the most abundant cytoplasmic proteins in human eosinophils. Except for some myeloid leukemia cells, basophils, and minor T cell populations, galectin-10 is exclusively present in eosinophils in the human body. Galectin-10 forms Charcot-Leyden crystals, which are observed in various eosinophilic diseases. Accumulating studies have indicated that galectin-10 acts as a new biomarker for disease activity, diagnosis, and treatment effectiveness in asthma, eosinophilic esophagitis, rhinitis, sinusitis, atopic dermatitis, and eosinophilic granulomatosis with polyangiitis. The extracellular release of galectin-10 is not mediated through conventional secretory processes (piecemeal degranulation or exocytosis), but rather by extracellular trap cell death (ETosis), which is an active cell death program. Eosinophils undergoing ETosis rapidly disintegrate their plasma membranes to release the majority of galectin-10. Therefore, elevated galectin-10 levels in serum and tissue suggest a high degree of eosinophil ETosis. To date, several studies have shown that galectin-10/Charcot-Leyden crystals are more than just markers for eosinophilic inflammation, but play functional roles in immunity. In this review, we focus on the close relationship between eosinophils and galectin-10, highlighting this protein as a potential new biomarker in eosinophilic diseases.