SPDL1 and COVID-19: In COVID-19 patients serum levels of sPD-L1 were significantly and negatively correlated with both total number of lymphocytes (Spearman’s rho -0.3353, p=0.0401) (Figure 2A) and levels of PaO2/FIO2 (Spearman’s rho -0.3274, p=0.0755) (Figure 2B).