Bactericidal permeability-increasing protein (BPI) is a 57-kDa cationic antimicrobial protein that is present principally in the azurophilic granules of polymorphonuclear leukocytes (Elsbach P 1998). BPI has both heparin- and LPS-binding capacity and displays anti-inflammatory activity and direct bactericidal action toward Gram-negative bacteria (Ooi CE et al. 1991; Weiss J et al. 1992; Levy O et al. 2000). Direct bactericidal activity and lipopolysaccharide neutralization are mediated by the N-terminal part of the protein, whereas the C-terminal region has been shown to opsonize bacteria (Iovine NM et al. 1997; Elsbach P & Weiss J 1998).
Antineutrophil cytoplasmic autoantibodies against BPI (BPI-ANCA) have been found in diseases of different etiologies, such as cystic fibrosis, TAP deficiency or inflammatory bowel diseases (Walmsley RS et al. 1997; Schultz H et al. 2004; Schinke S et al. 2004; Aichele D et al. 2006). The presence of BPI-ANCA has been shown to correlate with the chronic or profuse exposure of the host to Gram-negative bacteria and their endotoxin (Aebi C et al. 2000; Carlsson M et al. 2003; Schultz H et al. 2003; Schultz H 2007).