Indeed, although the timing of Ig production (from 4 days after symptoms onset to 10–14 days) limits its applicability for COVID-19 diagnosis in the acute phase [28,126], the detection of anti-SARS-CoV-2 IgM and/or IgA antibodies may represent an important tool for recognizing patients with the RT-PCR negative gap. The gene discussed is CD40LG; the disease is COVID-19.