MPO and systemic lupus erythematosus: Of the seven autoantigens, six markers were also upregulated during active SLE, however, MPO (3.4 ± 0.3 vs 0.9 ± 0.2 LogFC; p-value <0.0001), PRTN3 (2.9 ± 0.5 vs 1.2 ± 0.4 LogFC; p-value = 0.007), and PADI4 (1.8 ± 0.3 vs 0.4 ± 0.2 LogFC; p-value = 0.04) levels were significantly higher in severe COVID-19 blood (Figure 1D).