In comparison to severe acute respiratory syndrome coronavirus (SARS-CoV), SARS-CoV-2 appears to be more contagious [1], and coronavirus disease 2019 (COVID-19) patients demonstrate varied clinical manifestations distinct from those seen in patients with SARS-CoV and Middle East respiratory syndrome coronavirus infections [2]. Collective results from the clinical and epidemiological observations suggest a distinct viral-host interaction in COVID-19 patients. Profiling of the antibody response during SARS-CoV-2 infection may help improve our understanding of the viral-host interaction and the immunopathological mechanisms of the disease. Studies on humoral responses to infections have been mainly geared toward the production of high-affinity IgG antibodies that efficiently resolve an infection. It has been well recognised, however, that humoral immune response to infection can be a double-edged sword that either serves as a protective mechanism to resolve the infection or aggravates the tissue injury, e.g. the IgG response causes fatal acute lung injury by skewing the inflammation-resolving response in SARS-CoV [3]. In the case of respiratory infection, while IgM and IgG isotypes have been the primary emphasis in characterising immunity, mucosal and systemic IgA responses that may play a critical role in the disease pathogenesis have received much less attention. This study was designed to better understand the timing and patterns of humoral immune responses to SARS-CoV-2 in a cohort of COVID-19 patients and evaluate their relationship with the disease course and severity. 37 patients with COVID-19, with a mean±SD age of 52.3±16.3 years, were enrolled in this study. The enrolled COVID-19 patients consisted of 25 (67.6%) males and 12 (32.4%) females. All patients tested positive for viral nucleic acid of SARS-CoV-2 (Real-Time Fluorescent RT-PCR Kit; BGI, Shenzhen, China). According to the "Guidelines for the Diagnosis and Treatment of Novel Coronavirus (2019-nCoV) Infection" published by the National Health Commission of China, the enrolled COVID-19 patients were categorised into two groups: 20 (54.1%) severe cases and 17 (46.0%) nonsevere cases [4]. The nonsevere group included patients with mild and moderate symptoms who were also required to be admitted to hospital by the COVID-19 control policy in China. The severe group included severe and critically ill patients. Mild patients did not demonstrate abnormal computed tomography (CT) imaging. Moderate patients had fever and/or classical respiratory symptoms, and typical CT images of viral pneumonia. Severe patients met at least one of following additional conditions: 1) shortness of breath with a respiratory rate ⩾30 times•min −1 ; 2) oxygen saturation measured by pulse oximetry (resting state) of ⩽93%; or 3) arterial oxygen tension/inspiratory oxygen tension of ⩽300 mmHg. Critically ill patients met at least one of the extra following conditions in addition to the COVID-19 diagnosis: 1) respiratory failure that required mechanical ventilation; 2) shock; or 3) mu...

Coronavirus disease 2019 (COVID-19) is a highly contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has aroused great public health concern worldwide. Currently, COVID-19 epidemic is spreading in many countries and regions around the world. However, the study of SARS-CoV-2 is still in its infancy, and there is no specific therapeutics. Here, we summarize the genomic characteristics of SARS-CoV-2. In addition, we focus on the mechanisms of SARS-CoV-2 infection, including the roles of angiotensin converting enzyme II (ACE2) in cell entry, COVID-19 susceptibility and COVID-19 symptoms, as well as immunopathology such as antibody responses, lymphocyte dysregulation, and cytokine storm. Finally, we introduce the research progress of animal models of COVID-19, aiming at a better understanding of the pathogenesis of COVID-19 and providing new ideas for the treatment of this contagious disease.

Coronavirus disease 2019 (COVID-19) is a global pandemic infectious disease caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), and currently affects more than 8 million people worldwide. SARS-CoV-2 mainly invades the cells by binding to the angiotensin converting enzyme 2 (ACE2) receptor, leading to the injury of respiratory system, cardiovascular system, digestive system, and urinary system, and even secondary to acute respiratory distress syndrome (ARDS) and systemic inflammatory response, resulting in multiple organ failure. In this review, mainly focusing on biogenesis and pathogenic mechanisms, we describe the recent progress in our understanding of SARS-CoV-2 and then summarize and discuss its crucial clinical characteristics and potential mechanism in different systems. Additionally, we discuss the potential treatments for COVID-19, aiming at a better understanding of the pathogenesis of SARS-CoV-2 and providing new ideas for the personalized treatment of COVID-19.