CD40LG and viral infectious disease: The serological test for the presence of antibodies (IgM or IgG) against SARS-CoV-2 can provide a more accurate estimate of the cumulative prevalence of SARS-CoV-2 infection in a population since the beginning of the outbreak, compared to the molecular test (RT-PCR), in particular IgG resigned for past exposure, are likely to persist for a longer period of time after the viral infection is cleared.