CD4 and COVID-19: In the present study, we investigated how reductions in IFN1 signaling affect (1) the suppression of viral replication, (2) the migration of APCR and CTLL, (3) and (4) the differentiation of CD4+T0 into Th1 and Tfh, and consequently the severity of COVID-19 (STAR Methods, Table 4, Model 3, 4).