Anti-neutrophil cytoplasmic antibodies (ANCA) against bactericidal/permeability-increasing protein (BPI) and cystic fibrosis lung disease

Abstract

Persistent infection with Pseudomonas aeruginosa and inflammatory mechanisms play an important role in cystic fibrosis (CF) lung disease. ANCA against BPI, a potent host defence protein with anti-bacterial and anti-endotoxin properties, have been described in CF. We have assessed the relationship of anti-BPI antibodies to pulmonary disease severity in 148 CF subjects. IgA and IgG anti-BPI antibodies were found in 55.4% and 70.3% of CF patients, respectively, and higher levels were strongly associated with colonization with P. aeruginosa (P = 0.001 and 0.039 for IgA and IgG antibodies, respectively). IgA and IgG anti-BPI antibodies were independently associated with more severe lung disease as assessed by chest radiograph score (P = 0.023) and a significantly lower forced expiratory volume in 1 s (FEV1)% (P = 0.01). The pathophysiological relevance of the autoantibodies was investigated further by determining their epitope specificity and their effect on bacterial phagocytosis in vitro. Both isotypes of anti-BPI antibodies were specific for the C-terminus of BPI shown recently to be important for BPI-mediated opsonization, and in vitro affinity-purified anti-BPI antibodies significantly reduced BPI-induced phagocytosis of Escherichia coli compared with controls. These data indicate that anti-BPI autoantibodies are associated with colonization with P. aeruginosa and worse lung disease in CF. The inhibition of bacterial phagocytosis suggests that these autoantibodies may contribute to the persistence of P. aeruginosa in the CF lung and so play a role in perpetuating CF lung damage.

Fig. 1

Schematic representation of the parent and fusion proteins (adapted from Abrahamson et al. [18]). Text to the left of the schematics indicates the designation of the protein. Labels within parentheses indicate the portions of either the BPI or LBP proteins, and numbers indicate the amino acid positions. Black regions represent amino acid sequences derived from LBP protein. The letter N indicates the N terminus of the protein, and C indicates the C terminus.

Fig. 2

Graph showing the levels of IgA and IgG anti-BPI autoantibodies in patients not colonized with Pseudomonas aeruginosa (A) and those patients colonized with P. aeruginosa (B). The bar (–) indicates the median values and the dashed line (–––––) indicates the cut off for a positive result.

Fig. 3

Graph showing the binding of CF patients' sera (n = 85) to recombinant proteins 4160 (□) (containing the carboxyl terminal domain of BPI fused with the amino terminal domain of LBP) with rBPI50 (r = 0.88, P < 0.001); and 4161 (▪) (containing the amino terminal domain of BPI fused with the carboxyl terminal domain of LBP) with rBPI50 (r = 0.06, P > 0.05). Therefore a significant correlation of binding was seen between recombinant protein 4160 and the intact protein rBPI50.

Fig. 4

Bar chart of a representative set of values from three repeated experiments showing the inhibitory effect of 1, 10 and 100 μg/ml of affinity-purified anti-BPI antibodies on BPI-mediated phagocytosis of Escherichia coli from a patient with CF. Phagocytosis was significantly less (P < 0.005) for all concentrations of anti-BPI compared with the control.