Director of Infectious Diseases, Professor, Chief Physician, and Doctoral Supervisor. Specializes in the diagnosis and treatment of fever of unknown origin and various infectious diseases. Dr. Li has long been committed to the clinical diagnosis, treatment, and basic immunological research of infectious diseases. Over the past 30 years, with the support of major national infectious disease projects, he has made significant contributions to the clinical diagnosis, treatment, and immunological research of HIV/AIDS in China. In 1998, he was the first in the world to discover that antiviral therapy could reconstruct the CD4+ T cell function of AIDS patients, laying an important foundation for the theory of AIDS immune reconstruction. Based on this, he pioneered a comprehensive diagnosis, treatment, and full-process management model for HIV/AIDS antiviral therapy suitable for China's national conditions, forming the 'Chinese Plan' for AIDS antiviral therapy and immune reconstruction, which has been promoted and applied in China and developing countries. This fundamentally changed the low level of clinical treatment for AIDS in China and achieved a series of innovative results domestically and internationally, which were selected as one of the 'Top Ten Scientific and Technological Achievements' in the 60 years since the establishment of the Chinese Academy of Medical Sciences. During the COVID-19 pandemic, he served as an expert in the national medical treatment group for COVID-19, captain of the second batch of medical teams from Peking Union Medical College Hospital sent to Hubei, and head of the hospital's epidemic supervision group. He led nearly 30 experts in the hospital to discuss and formulate the 'Peking Union Medical College Hospital Diagnosis and Treatment Proposal for Novel Coronavirus Pneumonia (V2.0)', which was highly praised by the industry and promoted internationally. During his frontline anti-epidemic work in Wuhan, he discovered and proposed the immune pathogenesis of COVID-19 and its three-stage disease course. He also discovered the hypercoagulable and over-immune activation state of COVID-19 patients and proposed an effective solution of intravenous immunoglobulin combined with low molecular weight heparin, reducing the mortality rate of severe and critically ill patients. He stayed in Wuhan for 81 days until local COVID-19 cases were cleared.