Sialodochitis fibrinosa: Salivary duct obstruction by eosinophil extracellular traps?

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.

Confirmation of eosinophilic sialodochitis by terminal duct biopsy

OBJECTIVE

To analyse the histopathological features of eosinophilic sialodochitis by using terminal duct biopsy.

METHODS

Sixty-five patients with suspected eosinophilic sialodochitis and four with chronic obstructive sialadenitis were prospectively enrolled. Clinical features, laboratory tests and sialograms were comparatively analysed. Terminal duct biopsy of the parotid or submandibular glands was performed concomitantly with endoscopy-assisted duct dilatation to determine the histopathological features of eosinophilic sialodochitis.

RESULTS

Based on eosinophil quantification, the samples of suspected patients were scored as 'definite', 'highly suspected' and 'negative' in 26 (40%), 15 (23.1%) and 24 (36.9%) cases, respectively. Gland types and peripheral blood eosinophil counts were significantly different among these three groups. The proportions of itching glands, mucus plug exudations and elevated immunoglobulin E levels were higher in the 'definite' group than in the other two groups; however, the intergroup differences were insignificant. The primary pathological features of eosinophilic sialodochitis were abundant eosinophils and lymphocytes infiltrated around the duct, degranulation of eosinophils, extensive fibrosis and scattered mastocytes. Periductal eosinophils were not found in cases of chronic obstructive sialadenitis.

CONCLUSION

Our findings suggest that terminal duct biopsy is safe and valuable for the pathological confirmation of eosinophilic sialodochitis, and can be used simultaneously with endoscopy-assisted duct dilatation.

Eosinophilic sialoadenitis in a patient with severe asthma: a case report

Activated eosinophils can infiltrate various tissues and cause inflammatory tissue damage. Asthma is a typical type of eosinophilic inflammatory disease that occurs in the respiratory system. Eosinophilic sialodochitis and sialoadenitis of the salivary gland are rare diseases clinically characterized by painful swelling. In this report, we present a 68-year-old woman with asthma who presented to our hospital with mandibular swelling. Her asthma had been well controlled with an inhaled combination of a corticosteroid and a long-acting β2 agonist, although she reported a past history of frequent asthma attacks and hospitalization. Laboratory investigation on admission revealed blood eosinophilia (2,673/μL), high levels of total immunoglobulin E (390 U/mL) and immunoglobulin G4 (183 mg/dL). Bone marrow examination showed no evidence of eosinophilic neoplasia. Histological examination of her minor salivary glands disclosed an infiltration of mixed lymphocytes and eosinophils. Chromatolytic eosinophils with Charcot-Leyden crystals were also observed within the edematous dermis and fibrous tissues surrounding the minor salivary gland. The patient was diagnosed with eosinophilic sialoadenitis. Treatment with oral corticosteroids (0.5 mg/kg/day) was initiated. Thereafter, the mandibular swelling improved. This report describes a rare case of eosinophilic sialoadenitis in a patient with severe eosinophilic asthma, for which histopathological and immunefluorescence microscopic analyses were performed.

Eosinophil-mediated inflammation in the absence of eosinophilia

The increase of eosinophil levels is a hallmark of type-2 inflammation. Blood eosinophil counts act as a convenient biomarker for asthma phenotyping and the selection of biologics, and they are even used as a prognostic factor for severe coronavirus disease 2019. However, the circulating eosinophil count does not always reflect tissue eosinophilia and vice versa. The mismatch of blood and tissue eosinophilia can be seen in various clinical settings. For example, blood eosinophil levels in patients with acute eosinophilic pneumonia are often within normal range despite the marked symptoms and increased number of eosinophils in bronchoalveolar lavage fluid. Histological studies using immunostaining for eosinophil granule proteins have revealed the extracellular deposition of granule proteins coincident with pathological conditions, even in the absence of a significant eosinophil infiltrate. The marked deposition of eosinophil granule proteins in tissue is often associated with cytolytic degranulation. Recent studies have indicated that extracellular trap cell death (ETosis) is a major mechanism of cytolysis. Cytolytic ETosis is a total cell degranulation in which cytoplasmic and nuclear contents, including DNA and histones that act as alarmins, are also released. In the present review, eosinophil-mediated inflammation in such mismatch conditions is discussed.

Eosinophil extracellular traps in a patient with chronic eosinophilic pneumonia

Eosinophils rapidly release extracellular filamentous chromatin fibers (extracellular traps, ETs) when they are stimulated. Reticulated ETs have been recently shown to affect secretion viscosity in eosinophilic inflammatory diseases. Here we report a 43-year-old woman with infiltrative shadows in both upper lungs that did not respond well to antibiotics. She admitted to occasional coughing and sputum, but had poor viscous regulation. Bronchoalveolar lavage fluid (BALF) collected from the upper left lobe showed many eosinophils (65%). She was diagnosed with chronic eosinophilic pneumonia, per previously reported criteria, and began treatment with prednisolone. The infiltration shadow gradually improved, and she was discharged 28 days after admission. Later, we immune-stained her BALF cell components with antibodies against major basic protein, an eosinophil granule protein, which showed a large number of agglomerating eosinophils; and antibodies against citrullinated histone H3 (CitH3-a marker for ETs), which showed CitH3-positive ETs, spread in a network. These findings confirmed that some BALF eosinophils released eosinophil ETs. This case shows the existence of ETs from BALF in patients with chronic eosinophilic pneumonia. Concentration of eosinophil ETs in eosinophilic inflammatory diseases may affect secretion viscosity in sputum, and so on.

Eosinophilic sialodochitis: An emerging atopic condition

OBJECTIVE

To report the clinical characteristics of the largest single centre cohort of patients with eosinophilic sialodochitis.

METHODS

Analysis of data relating to 37 patients seen in a dedicated multidisciplinary clinic was performed. Demographic, clinical, haematological, cytological, histological and radiological features were collated. Response to trials of allergy treatment was assessed.

RESULTS

Thirty-seven patients (30 female, seven male) were identified, 42% of whom were of Afro-Caribbean origin, with a mean age of 50.4 years (range 28-80 years). Mean symptom duration at presentation was 10 years (range 2-33 years). Parotid and submandibular gland involvement was equally reported. The most commonly reported symptoms were swelling (97%), itching of the overlying skin (92%), salivary gland discomfort (84%) and "string-like" mucus discharge from salivary duct orifices (76%). Twenty-three patients (62%) demonstrated atopic disease and serum IgE level elevated in 57%. All 37 patients had eosinophils present in aspirated duct contents samples while raised peripheral eosinophil count was seen in 41%. Anecdotal symptom improvement was reported with antihistamine, antileukotriene or steroid treatment.

CONCLUSION

Eosinophilic sialodochitis should be considered in any patient presenting with recurrent salivary gland swelling. Further studies are needed to evaluate treatments directed at a likely allergic pathogenesis.

How to detect eosinophil ETosis (EETosis) and extracellular traps

Eosinophils are short-lived and comprise only a small population of circulating leukocytes; however, they play surprisingly multifunctional roles in homeostasis and various diseases including allergy and infection. Recent research has shed light on active cytolytic eosinophil cell death that releases eosinophil extracellular traps (EETs) and total cellular contents, namely eosinophil extracellular trap cell death (EETosis). The pathological contribution of EETosis was made more cogent by recent findings that a classical pathological finding of eosinophilic inflammation, that of Charcot-Leyden crystals, is closely associated with EETosis. Currently no gold standard methods to identify EETosis exist, but “an active eosinophil lysis that releases cell-free granules and net-like chromatin structure” appears to be a common feature of EETosis. In this review, we describe several approaches that visualize EETs/EETosis in clinical samples and in vitro studies using isolated human eosinophils. EETs/EETosis can be observed using simple chemical or fluorescence staining, immunostaining, and electron microscopy, although it is noteworthy that visualization of EETs is greatly changed by sample preparation including the extracellular space of EETotic cells and shear flow. Considering the multiple aspects of biological significance, further study into EETs/EETosis is warranted to give a detailed understanding of the roles played in homeostasis and disease pathogenesis.