title: Bactericidal/permeability-increasing protein (BPI) is an important antigen for anti-neutrophil cytoplasmic autoantibodies (ANCA) in vasculitis.
abstract: Indirect immunofluorescence (IIF) techniques have shown that ANCA are useful serological markers for some small vessel vasculitides, and ELISA assays, using purified molecules as solid-phase ligand, have helped to identify proteinase 3 (PR3) and myeloperoxidase (MPO) as two of the major ANCA antigens. There remain a substantial number of serum samples, which are positive by IIF, yet recognize neither PR3 nor MPO (double-negative samples). We found, by Western blot analysis of soluble neutrophil granule proteins, that certain of these double-negative samples recognized a 55-kD doublet of which the first eight residues shared N-terminal amino acid sequence homology with BPI, a potent antibiotic towards Gram-negative bacteria. We developed a simple, quick and robust two-step immunobiochemical method to purify BPI. This was then employed to detect anti-BPI autoantibodies by ELISA and Western blot analysis. We tested 100 double-negative samples and 400 consecutive new samples sent for routine ANCA testing in the anti-BPI ELISA. We found that 45 of the 100 double-negative and 44 of the 400 new routine samples recognized BPI. By Western blot analysis 20/20 positive anti-BPI samples blotted the 55-kD protein. Inhibition assays confirmed the specificity of binding. Review of the 89 anti-BPI-positive patients showed a male dominance (M:F ratio 55:34), a mean age of 60.4 years and clinical diagnoses ranging from organ limited vasculitis to widespread systemic vasculitis.
authors: Department of Medicine, School of Clinical Medicine, University of Cambridge, UK.
authors: M H
authors: MH
authors: Zhao
authors: S J
authors: SJ
authors: Jones
authors: C M
authors: CM
authors: Lockwood
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000595:Amino Acid Sequence; D019268:Antibodies, Antineutrophil Cytoplasmic; D023181:Antimicrobial Cationic Peptides; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology; D015415:Biomarkers / Q000097:blood; D001770:Blood Bactericidal Activity; D001798:Blood Proteins / Q000276:immunology / Q000302:isolation & purification*; D015153:Blotting, Western; D002648:Child; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D008565:Membrane Proteins; D008875:Middle Aged; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000737:chemistry; D014657:Vasculitis / Q000276:immunology*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D023181:Antimicrobial Cationic Peptides; D001323:Autoantibodies; D015415:Biomarkers; D001798:Blood Proteins; D008565:Membrane Proteins; C021623:bactericidal permeability increasing protein