Abstract
BACKGROUND: A better understanding of innate and adaptive cells in COVID-19 is necessary for the development of effective treatment methods and vaccines. METHODS: We studied phenotypic features of innate and adaptive immune cells, oxidative burst, phagocytosis, and apoptosis. One hundred and three patients with COVID-19 were grouped according to their clinical features into the categories of mild (35%), moderate (40.8%), and severe (24.3%). RESULTS: Monocytes were CD16(+) pro-inflammatory monocytes and tended to shed their HLA-DR, especially in severe cases (p < 0.01). Neutrophils were mature and functional, although a decline of their CD10 and CD16 was observed (p < 0.01). No defect was found in the reactive oxygen species production and their apoptosis. The percentage of natural killer cells was in the normal range, whereas the percentages of CD8(+) NK and CD56(+) T lymphocytes were found to be high (p < 0.01). Although the absolute numbers of all lymphocyte subsets were low and showed a tendency for a gradual decrease in accordance with the disease progression, the most decreased absolute number was that of B lymphocytes, followed by CD4(+) T cells in the severe cases. The percentages of double-negative T cells; HLA-DR(+) CD3(+) and CD28(-) CD8(+) subsets were found to be significantly increased. Importantly, we demonstrated the increased baseline activation of caspase-3 and increased lymphocyte apoptosis. CONCLUSION: We suggest that SARS-CoV-2 primarily affects the lymphocytes and not the innate cells. The increased baseline activation of Caspase-3 could make the COVID-19 lymphocytes more vulnerable to cell death. Therefore, this may interrupt the crosstalk between the adaptive and innate immune systems.