CD4 and COVID-19: With the aim to better understand the molecular mechanisms involved in the orderly shutdown and retraction of CD4+ type Th1 cell response, Chauss et al. recently analyzed the bronchoalveolar lavage fluid CD4+ T cells of patients with COVID-19 and identified an autocrine/paracrine vitamin D loop that allows Th1 cells to activate and respond to vitamin D as part of a complex shutdown program repressing IFN-γ and enhancing IL-10 [61].