CD4 and COVID-19: Research in adult patients has highlighted the importance of T lymphocytes, CD4+ T cells in particular, in controlling and fine-tuning the pathogenesis and outcomes of SARS-CoV and Middle East respiratory syndrome CoV infection.15 However, the function of B cells and antibodies is often ignored despite the fact that B cells also decreased among patients with COVID-19.20 In this study, the serum concentration of IgG was significantly decreased in moderate cases compared with mild cases.