The presence of autoantibodies in the blood circulation that react against bactericidal/permeability-increasing protein (BPI). BPI is an endotoxin-binding host protein with important antibacterial effects against Gram-negative bacteria, such as Pseudomonas aeruginosa. BPI is a 55 kDalton protein that is most abundant in the azurophilic granules of neutrophils. BPI also acts as a target antigen for antineutrophil cytoplasmic autoantibodies. [from HPO]