Ultrastructural Modification of Eosinophils in BALF of SARS-CoV-2 Patients

This chapter investigates the infectivity and ultrastructural alterations in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected eosinophils isolated from the bronchoalveolar lavage fluid (BALF) of coronavirus disease 2019 (COVID-19) patients across different age groups. Imaging techniques, including immunofluorescence (IF), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), have been employed to characterize the ultrastructural modifications in eosinophils from both young and elderly COVID-19 patients, particularly those with common comorbidities, such as diabetes, liver disease, kidney disease, and malignancies. The observed ultrastructural changes include an irregular cell surface, cytoplasmic degeneration, degranulation of eosinophilic granules, and virus-like particles, both intracellularly and on the cell membrane. Notably, eosinophils from COVID-19 patients without comorbidities exhibit a higher viral load than those with underlying conditions. Among the comorbid groups, diabetic patients display the most extensive ultrastructural damage. Interestingly, younger COVID-19 patients (≤60 years) demonstrate a higher infectivity than older patients (≥60 years), suggesting that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogenicity is closely linked to both age and preexisting health conditions.