CD40LG and COVID-19: The MSAT cohort includes healthy, well-trained males recruited for exercise tests conducted at the Department of Clinical Sciences, Malmö, Lund University, with the characteristics of age 37.4 ± 8.3 years [mean ± SD], BMI 24.4 ± 2.4 kg/m2 [mean ± SD], and VO2MAX = 52.0 ± 8.1 ml/kg/min [mean ± SD].Thirty-nine serum samples collected between 2016 and 2017 were tested for COVID-19 IgM/IgG reactivity.