The levels of bactericidal/permeability increasing protein (BPI) in body fluids

Abstract

Rationale BPI is a microbicidal protein detected in neutrophil granules and recently discovered in epithelia. BPI, together with LBP (lipopolysaccharide binding protein) and CD14, binds with high affinity LPS (lipopolysaccharide). BPI is the target of autoantibodies, BPI-ANCA being found in a subset of patients with cystic fibrosis (CF), autoimmune hepatitis, and rheumatoid arthritis. To test the hypothesis that ANCA might develop related to chronic exposure to excess target antigen derived from the epithelia, we investigated the levels of BPI in body fluids. Methods BPI serum levels were measured in 41 children who were CF BPI-ANCA negative, 39 who were BPI-ANCA positive, and 40 controls. Ten eluates from CF stools and 10 controls were also investigated for BPI presence and saliva samples were screened for BPI content. Results Serum levels of BPI did not differ in the tested subgroups of BPI-ANCA negative children (58.5 ng/ml), BPI-ANCA positive children (61.8 ng/ml) or controls (56.1 ng/ml). Only 2 CF and 1 normal stool eluate had very low levels of BPI. Saliva levels of BPI were remarkably stable, 77.4-78.9 ng/ml in all tested subject, with no difference between CF and controls. Conclusions Circulating BPI is stable and does not correlate with BPI-ANCA or clinical disease status. BPI most probably of epithelial origin is consistently present in saliva.