In a prospective diagnostic study, Deirmengian and colleagues found that the concentration in the synovial fluid of antimicrobial factors, such as α-defensin, neutrophil elastase (ELA-2), bactericidal permeability-increasing protein (BPI), lactoferrin, and neutrophil gelatinase-associated lipocalin (NGAL), increased in PJI patients, thus suggesting that these factors are biomarkers of the infection [9]. This evidence concerns the gene BPI and infection.