Brinkmann et al [9] first reported in 2004 that when the body is infected by pathogens, neutrophils can release cell-free DNA (cf-DNA) as the basic extracellular framework, along with citrullinated histones 3 (citH3), myeloperoxidase (MPO), neutrophil elastase (NE), and antimicrobial peptide LL-37 (CAMP, LL37) during pathogen infection to form net-like structures known as neutrophil extracellular traps (NETs). Here, MPO is linked to infection.