Members of the bactericidal/permeability-increasing protein family have antimicrobial properties and bind lipophilic substances, therefore targeting gram-negative bacteria. The bactericidal permeability increasing protein (BPI) is an antibacterial and endotoxin-neutralizing molecule that is abundant in the granules of polymorphonuclear leukocytes (neutrophil granules). Sharing structural and sequence homologies with BPI, BPIL1 (bactericidal/permeability-increasing protein-like 1) is a 458 amino acid secreted protein that contains the family’s common conserved feature of two cysteine residues that are critical for protein function.