BPI‐ANCA of pediatric cystic fibrosis patients can impair BPI‐mediated killing of E. coli DH5α in vitro

Abstract

Gram-negative bacterial lung infections and chronic bacterial colonization are major threats for pediatric cystic fibrosis (CF) patients. Besides impeded mucociliary clearance, other mechanisms that contribute to increased susceptibility to infections are presumed. The bactericidal/permeability-increasing protein (BPI), which is delivered by neutrophil granulocytes and mucosal epithelial cells, is one of the most potent innate antibiotics against Gram-negative bacteria and endotoxin. Antineutrophil cytoplasmic autoantibodies against BPI (BPI-ANCA) have been found in up to 90% of CF patients, and titers correlated inversely with lung function parameters. As major pulmonary damage is mediated by Gram-negative bacteria and their products, the question was raised as to whether BPI-ANCA can inhibit the antibiotic function of BPI in these patients. Sera of 23 pediatric CF patients were analyzed for the presence of BPI-ANCA by indirect immunofluorescence, ELISA, epitope mapping, and Western blotting. Patients' IgG were tested in a bacterial growth inhibition assay with recombinant BPI (rBPI) and an amino-terminal fragment of BPI (rBPI(21)) that retains antibiotic activity for inhibition of the antibiotic function of BPI against E. coli DH5alpha in vitro. BPI was recognized by 21 of 23 patients' sera in our detection assays. Thirteen of 23 patients' BPI-ANCA (56%) could inhibit the antibiotic function in vitro. Moreover, epitope mapping over the whole BPI sequence revealed that more patients' BPI-ANCA recognize the amino-terminal part of BPI than can be detected by ELISA. Thus, in pediatric CF patients, BPI-ANCA may contribute to diminished bacterial clearance by inhibiting the antibiotic function of BPI.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

“…Epitope mapping data have revealed similarities of BPI epitopes recognized by BPI-ANCA (Table 1) with specific protein sequences of infecting GNB (e.g. outer membrane proteins of Pseudomonas aeruginosa) suggesting that cross-reactivity followed by epitope spreading in the inflammatory setting could be a mechanism for broken tolerance against BPI [118,119]. The waning of BPI-ANCA in CF patients after lung transplantation and a reduced pulmonary burden of P. aeruginosa [120,121] is consistent with this hypothesis.…”

“…In contrast, BPI bound endotoxin is not accessible for LBP/CD14 mediated LOS/LPS extraction and does not cause an inflammatory response in monocytes [81,82,107]. Shown is the prevalence of BPI-ANCA in selected studies of healthy persons and patients with infectious diseases, rheumatic diseases, inflammatory bowel diseases and immunodeficiency [17,18,115,118,119,126]. Abbreviations: HIV human immunodeficiency virus; ReA reactive arthritis; TAP transporter associated with antigen presentation…”

“…The correlation of BPI-ANCA levels in CF and IBD patients indicate that BPI-ANCA might be useful to identify subgroups of patients with higher inflammatory activity and more severe organ damage (Table 2, [16,[117][118][119][120][121][122]). The ability of BPI-ANCA to interfere with the opsonic [123] and antibiotic [18,119,124] actions of BPI has been demonstrated in vitro.…”

Expression and Antimicrobial Function of Bactericidal Permeability-Increasing Protein in Cystic Fibrosis Patients

“…It has been suggested that BPI plays a crucial role during P. aeruginosa lung infections in CF patients (8,23,24,22). Nevertheless, to date, there are no data available on the expression of BPI in the infected lungs of CF patients.…”

“…Recently, a mouse ortholog of human BPI was described, indicating the importance of this antimicrobial protein throughout evolution in different vertebrate species (7). Antineutrophil cytoplasmic autoantibodies against BPI (BPI-ANCA) have been found in up to 90% of CF patients (22,28), and the presence of BPI-ANCA has been shown to correlate with chronic P. aeruginosa lung infection (1,6) and Pseudomonas-induced lung damage (4). In vitro, BPI-ANCA have been shown to inhibit neutrophil-mediated killing of P. aeruginosa (24).…”