CD40LG and infectious disease: The median IgM level in the convalescent-phase serum samples of COVID-19 patients (0.95, IQR = 0.81–1.17) was significantly higher than in healthy donors (0.78, IQR = 0.71–0.85) and patients with other infectious disease (0.81, IQR = 0.73–0.87, both P < 0.05, Fig 3A).