CD40LG and infection: Previous studies have shown that the SARS-CoV-2 antigen stimulates the immune system to produce an immune response and that specific IgM and IgG antibodies appear in the serum of patients after infection.4 The SARS-CoV-2-specific IgM and IgG antibody tests have been involved in the diagnosis criteria for suspected patients whose COVID-19 viral nucleic acid test appears false negative, according to the recently published guidelines of Novel Coronavirus Pneumonia Diagnosis and Treatment (Trial Version 7), which were advocated by the National Health Committee.5