A microscopy study to distinguish the ultrastructural changes in the ciliated epithelium, type II pneumocytes, macrophages, and neutrophils of bronchoalveolar fluids after severe SARS-CoV-2 infection

Abstract

SARS-CoV-2 infection has an adverse effect on the functioning of various respiratory and hematopoietic cells in the bronchoalveolar fluid (BALF) resulting from ultrastructural alterations. These ultrastructural changes were directly corroborated to understand the altered function of these cells. These changes have been sparingly reported and it is important for understanding the biology of COVID-19. We have reported various ultrastructural alterations of ciliated epithelium, type II pneumocytes, macrophages, and neutrophils individually from the BALF of patients with severe COVID-19. Ultrastructural alterations depend on various conditions such as age, immunity, associated comorbidities, disease severity, and medication received by patients. The ciliated epithelium mostly contained viral-containing compartments, horseshoe-shaped mitochondria, necrosis, and double-membrane vesicles. Type II pneumocyte cells showed cytoplasmic vacuolization, loss of lamellar bodies, and the formation of viral inclusion bodies. The alveolar macrophages displayed increased size and number of phagocytic vacuoles containing viral particles (phagosomes) and vacuolated cytoplasm. Neutrophils showed cytoplasmic granularity, vacuolization, and the presence of extracellular traps. This study provides important insights into the cellular and morphological changes associated with COVID-19 in BALF cells.