CD83 and COVID-19: In sharp contrast, pDCs from severe COVID-19 patients failed to be activated by SARS-CoV-2-infected cells, as demonstrated by the absence or low detection of IFN-α, IFN-λ, CD83, and CD80/PD-L1 as compared to healthy donors and mild/asymptomatic patients (Fig. 2c–h; red bars and arrows).