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<b><i>Background:</i></b> Although the pathophysiology of coronavirus disease 2019 (COVID-19) is not clearly defined, among the proposed mechanisms, immune system dysfunction is more likely than others. The aim of this study was to clarify the characteristics and clinical significance of dynamic changes of lymphocyte subsets in the course of COVID-19. <b><i>Methods:</i></b> In this prospective study, the levels of peripheral lymphocyte subsets including CD4⁺, CD8⁺, CD4⁺CD25⁺FOXP3⁺, CD38⁺, CD3⁺HLA-DR⁺, CD19⁺, CD20⁺, and CD16⁺CD56⁺ cells were measured by flow cytometry in 52 confirmed hospitalized patients with COVID-19 at the day of admission and after 7 days of care. Clinical response was defined as improvement in symptoms (fever, dyspnea, and cough as well as blood oxygen saturation), and patients who met these criteria after 1 week of admission were classified as early responders; others who survived and finally discharged from the hospital were classified as late responders and patients who died were categorized as nonresponders. Immunophenotyping of studied cell changes on the first day of admission and 7 days after treatment were compared. Besides, the correlation between cellular subset variation and clinical response and outcome were analyzed. <b><i>Results:</i></b> Total counts of white blood cell, T cells, CD4⁺ T cells, CD8⁺ T cells, CD38⁺ lymphocytes, and CD3⁺HLA-DR⁺ lymphocytes were significantly increased in both early and late responders. No statistically significant difference was observed in CD4⁺/CD8⁺ ratio, B cells, FOXP3⁺<i>T</i>_reg lymphocytes, and FOXP3 median fluorescence intensity among studied groups. According to the multivariate analysis, an increase in CD4⁺ T cells (<i>p</i> = 0.019), CD8⁺ T cells (<i>p</i> = 0.001), and administration of interferon (<i>p</i> &#x3c; 0.001) were independent predictors of clinical response. <b><i>Conclusion:</i></b> We found an increasing trend in total T cells, T helpers, cytotoxic T cells, activated lymphocytes, and natural killer cells among responders. This trend was not statistically significant among nonresponders. The findings of this study may enhance our knowledge about the pathogenesis of COVID-19.

Background Since the outbreak of the novel coronavirus disease-2019 (COVID-19) in December 2019, limited studies have investigated the histopathologic findings of patients infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Material and methods This study was conducted on 31 deceased patients who were hospitalized for COVID-19 in a tertiary hospital in Tehran, Iran. A total of 52 postmortem tissue biopsy samples were obtained from the lungs and liver of decedents. Clinical characteristics, laboratory data, and microscopic features were evaluated. Reverse transcription polymerase chain reaction (RT-PCR) assay for SARS-CoV-2 was performed on specimens obtained from nasopharyngeal swabs and tissue biopsies. Results The median age of deceased patients was 66 years (range, 30–87 years) and 25 decedents (81 %) were male. The average interval from symptom onset to death was 13 days (range, 6–34 days). On histopathologic examination of the lung specimens, diffuse alveolar damage and thrombotic microangiopathy were the most common findings (80 % and 60 %, respectively). Liver specimens mainly showed macrovesicular steatosis, portal lymphoplasmacytic inflammation and passive congestion. No definitive viral inclusions were observed in any of the specimens. In addition, 92 % of lung tissue samples tested positive for SARS-CoV-2 by RT-PCR. Conclusions Further studies are needed to investigate whether SARS-CoV-2 causes direct cytopathic changes in various organs of the human body.