Cluster M3 was highly correlated to cluster M4 as indicated by a high Pearson correlation coefficient (r = 0.92; Supplementary Table S1L) between the 2 clusters, and contains proteins with a similar alteration in COVID-19 cohorts (eg, VWF, leucine-rich α2-glycoprotein 1, galectin-1, and polymeric immunoglobulin receptor). This evidence concerns the gene PIGR and COVID-19.