1. Patients aged from 18 to 80 years, 2. conformed to epidemic history, 3. fever and respiratory symptoms, 4. normal or decreased leukocyte count in peripheral blood, or decreased lymphocyte count, 5. conformed to imaging features of COVID-19 pneumonia, 6. positive for COVID-19 nucleic acid test or second-generation sequencing of pathogens, 7. serum KL- 61500U / ml, 8. and conforms to any of the following: (1) respiratory distress, RR >=30 beats / min, (2) oxygen saturation <=93% at rest, (3) partial pressure of arterial oxygen (PaO2) / oxygen concentration (FiO2) <=300mmHg (1mmHg=0.133kPa).

1. Patients aged from 18 to 80 years, 2. conformed to epidemic history, 3. fever and respiratory symptoms, 4. normal or decreased leukocyte count in peripheral blood, or decreased lymphocyte count, 5. conformed to imaging features of COVID-19 pneumonia, 6. positive for COVID-19 nucleic acid test or second-generation sequencing of pathogens, 7. serum KL- 61500U / ml, 8. and conforms to any of the following: (1) respiratory distress, RR >=30 beats / min, (2) oxygen saturation <=93% at rest, (3) partial pressure of arterial oxygen (PaO2) / oxygen concentration (FiO2) <=300mmHg (1mmHg=0.133kPa).