C9 and infection: To further identify biomarkers associated with infection severity in IE, we screened proteins with the top 20 feature importance using an ML-based classifier to distinguish the double-positive category from the double-negative category, which included 11 upregulated proteins (e.g., C9 and LRG1) and 9 downregulated proteins, such as VPS25 and ferritin light chain (FTL), in the double-positive group (Fig. 5D, E).