BACKGROUND. Since December 2019, an outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, and is now becoming a global threat. We aimed to delineate and compare the immunological features of severe and moderate COVID-19. METHODS. In this retrospective study, the clinical and immunological characteristics of 21 patients (17 male and 4 female) with COVID-19 were analyzed. These patients were classified as severe (11 cases) and moderate (10 cases) according to the guidelines released by the National Health Commission of China. RESULTS. The median age of severe and moderate cases was 61.0 and 52.0 years, respectively. Common clinical manifestations included fever, cough, and fatigue. Compared with moderate cases, severe cases more frequently had dyspnea, lymphopenia, and hypoalbuminemia, with higher levels of alanine aminotransferase, lactate dehydrogenase, C-reactive protein, ferritin, and D-dimer as well as markedly higher levels of IL-2R, IL-6, IL-10, and TNF-α. Absolute numbers of T lymphocytes, CD4⁺ T cells, and CD8⁺ T cells decreased in nearly all the patients, and were markedly lower in severe cases (294.0, 177.5, and 89.0 × 10⁶/L, respectively) than moderate cases (640.5, 381.5, and 254.0 × 10⁶/L, respectively). The expression of IFN-γ by CD4⁺ T cells tended to be lower in severe cases (14.1%) than in moderate cases (22.8%). CONCLUSION. The SARS-CoV-2 infection may affect primarily T lymphocytes, particularly CD4⁺ and CD8⁺ T cells, resulting in a decrease in numbers as well as IFN-γ production by CD4⁺ T cells. These potential immunological markers may be of importance because of their correlation with disease severity in COVID-19. TRIAL REGISTRATION. This is a retrospective observational study without a trial registration number. FUNDING. This work is funded by grants from Tongji Hospital for the Pilot Scheme Project, and partly supported by the Chinese National Thirteenth Five Years Project in Science and Technology for Infectious Disease (2017ZX10202201).

To improve the diagnostic efficacy of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for Chinese patients with fever of unknown origin (FUO) and inflammation of unknown origin (IUO), with combined clinical parameters. FUO/IUO patients who underwent a standard diagnostic work-up and 18F-FDG PET/CT scanning were enrolled and divided into a local uptake lesion subgroup and a non-specific abnormal uptake subgroup. Beneficial clinical parameters for improving the diagnostic efficacy of PET/CT were identified. From January 2014 to January 2019, 253 FUO/IUO patients were studied. In total, 147 patients had local uptake lesions and 106 patients had non-specific abnormal uptake. In the local uptake lesion group, the positioning accuracy of PET/CT was 37.2% in grades 1 and 2, and 66.3% in grades 3 and 4. With the following combination of clinical parameters, the positioning accuracy increased to 75.0% and 90.0%, respectively: time from admission to performing PET/CT scanning 95 mg/l. In the non-specific abnormal uptake group, the combination of sex (male), bicytopenia, and lactic dehydrogenase improved the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing malignancy from 64.3%, 69%, 60%, and 72.7%, respectively, to 83.3%, 81%, 81.4%, and 82.9%, respectively. With the combination of sex (male), white blood count, serum ferritin level, and hepatosplenomegaly, the infection prediction model had a sensitivity, specificity, PPV, and NPV of 78%, 76.2%, 76.6%, and 77.6%, respectively. Combined clinical parameters improved the localization diagnostic value of 18F-FDG PET/CT in the local uptake lesion subgroup and the etiological diagnostic value in the non-specific abnormal uptake subgroup.