Rezaei M, Marjani M, Mahmoudi S, et al. - In view of the uncertainty regarding the pathophysiology of coronavirus disease 2019 (COVID-19), and the higher likelihood of immune system dysfunction than others among the proposed mechanisms, researchers sought to ascertain the characteristics and clinical significance of dynamic changes of lymphocyte subsets in the course of COVID-19. Improvement in symptoms (fever, dyspnea, and cough as well as blood oxygen saturation) was defined as clinical response. Assessment of 52 confirmed hospitalized patients with COVID-19 at the day of admission and after 7 days of care by flow cytometry revealed significantly increased total counts of white blood cell, T cells, CD4+ T cells, CD8+ T cells, CD38+ lymphocytes, and CD3+HLA-DR+ lymphocytes in both early and late responders. Hence responders exhibited an increasing trend in total T cells, T helpers, cytotoxic T cells, activated lymphocytes, and natural killer cells. Among nonresponders, this trend was not identified as statistically significant. The findings of this study may elaborate the insight concerning the pathogenesis of COVID-19.