TNF and COVID-19: However, both severe (7.18 ± 0.94 pg/ml, P<0.0001) and mild (5.73 ± 0.26 pg/ml, P<0.0001) COVID-19 patients had significantly higher serum TNF-α concentrations than healthy subjects (0.2 ± 0.03 pg/ml) (Table 2, Figure 1D).