To determine whether OC43 infection can also induce a CD4+ T cell response that cross-reacts with SARS-CoV-2, HLA-DRB1*0101 Ifnar1−/− mice were infected with OC43, and spleens and lungs harvested on days 8, 16, and 30 post-infection (Fig. 4A). This evidence concerns the gene CD4 and infection.