CD40LG and COVID-19: Moreover, the extremely low positive rate of human CoV RNA tests by RT-PCR in tears and conjunctival secretions from patients with SARS and CoVID-19 may be related to the relatively low sensitivity of the current RT-PCR technique, later timing sample collection, and the activation of the host immune system and significant increases in lactoferrin and secretory IgA levels in tears and in circulating IgM and IgG levels in plasm.