Atypical lymphocytes in bronchoalveolar lavage fluid from patients with COVID-19 ARDS

Coronavirus disease 2019 (COVID-19): Focus on peripheral blood cell morphology

Numerous studies have shown peculiar morphological anomalies in COVID-19 patients' smears. We searched all the peer-reviewed scientific publications that explicitly reference the cytomorphological alterations on peripheral blood smears of patients with COVID-19. We extracted data from sixty-five publications (case reports, patient group studies, reviews, and erythrocyte morphology studies). The results show that frequent alterations concern the morphology of lymphocytes (large lymphocytes with weakly basophilic cytoplasm, plasmacytoid lymphocytes, large granular lymphocytes). Neutrophils display abnormal nuclei and cytoplasm in a distinctive cytomorphological picture. Besides a left shift in maturation, granulations can be increased (toxic type) or decreased with areas of basophilia. Nuclei are often hyposegmented (pseudo-Pelger-Huёt anomaly). Apoptotic or pycnotic cells are not uncommon. Monocytes typically have a large cytoplasm loaded with heterogeneous and coalescing vacuoles. Platelets show large and giant shapes. The presence of erythrocyte fragments and schistocytes is especially evident in the forms of COVID-19 that are associated with thrombotic microangiopathies. Such atypia of blood cells reflects the generalized activation in severe COVID-19, which has been demonstrated with immunophenotypic, molecular, genetic, and functional methods. Neutrophils, in particular, are involved in the pathophysiology of hyperinflammation with cytokine storm, which characterizes the most unfavorable evolution.

Cytopathological Findings in Bronchoalveolar Lavage from Patients with COVID-19

Information on cellular analysis of bronchoalveolar lavage (BAL) in patients with COVID-19 is limited. Some studies have described an increase in lymphocyte percentage or exuberant plasmacytosis. Some reports addressed the importance of molecular testing on BAL samples to confirm COVID-19 pneumonia, in clinically highly suspected patients with consecutive negative nasopharyngeal swab results. In addition to atypical lymphocytes in the peripheral blood, morphologic findings of atypical lymphocytes in BAL were also reported in a few patients. The objective of this study was to describe the cytopathic characteristics identified, any data presented here are descriptives and intended to trigger further research. Three general aspects have been evaluated in each sample: reactive changes, virus-related pathological changes, and differential leukocyte count. Seventeen samples were collected. All samples were negative for malignancy, with an inflammatory background, predominantly lymphohistiocytic in 5 samples, histiocytic in 9, and 3 with predominantly neutrophilic. Hemosiderin-laden macrophages were observed in 12/17. Nonspecific reactive cell changes were identified in 4 samples, including bronchial, alveolar, and reserve cell hyperplasia. Virus-related pathological changes were observed in 14 samples, such as loss of nuclear chromatin pattern, lymphocytes with atypical nuclei, nuclear and cytoplasmic inclusions, multinucleations in bronchial cells and macrophages, or multinucleated giant cells. The identification of multinucleated giant cells could represent a cytopathic effect induced by the virus, at the same time the nuclear clearance of pneumocytes as a possible direct effect. BAL is a procedure aimed at obtaining cells from the respiratory tract that can provide valuable and rapid information. It is important to collect and describe as many cytopathological findings as possible, which can provide relevant information for future studies.

Comprehensive evaluation of bronchoalveolar lavage from patients with severe COVID-19 and correlation with clinical outcomes

Information on bronchoalveolar lavage (BAL) in patients with COVID-19 is limited, and clinical correlation has not been reported. This study investigated the key features of BAL fluids from COVID-19 patients and assessed their clinical significance. A total of 320 BAL samples from 83 COVID-19 patients and 70 non-COVID-19 patients (27 patients with other respiratory viral infections) were evaluated, including cell count/differential, morphology, flow cytometric immunophenotyping, and immunohistochemistry. The findings were correlated with clinical outcomes. Compared to non-COVID-19 patients, BAL from COVID-19 patients was characterized by significant lymphocytosis (p < 0.001), in contrast to peripheral blood lymphopenia commonly observed in COVID-19 patients and the presence of atypical lymphocytes with plasmacytoid/plasmablastic features (p < 0.001). Flow cytometry and immunohistochemistry demonstrated that BAL lymphocytes, including plasmacytoid and plasmablastic cells, were composed predominantly of T cells with a mixture of CD4+ and CD8+ cells. Both populations had increased expression of T-cell activation markers, suggesting important roles of helper and cytotoxic T-cells in the immune response to SARS-CoV-2 infection in the lung. More importantly, BAL lymphocytosis was significantly associated with longer hospital stay (p < 0.05) and longer requirement for mechanical ventilation (p < 0.05), whereas the median atypical (activated) lymphocyte count was associated with shorter hospital stay (p < 0.05), shorter time on mechanical ventilation (p < 0.05) and improved survival. Our results indicate that BAL cellular analysis and morphologic findings provide additional important information for diagnostic and prognostic work-up, and potential new therapeutic strategies for patients with severe COVID-19.