CD40LG and COVID-19: Respiratory viruses generally enter the body through the nasal, oral, or conjunctival mucosa, and are mainly hindered by the IgA present in secretions; the virus-specific IgA-mediated immune response of the mucous membranes of COVID-19 patients appear to be detected in the majority of patients, and may be more effective and lasting than the IgM-mediated response [14].