The purpose of this study is to

examine the fine specificity of autoantibodies targeting MPO. This continuing effort could define epitopes that have pathogenic implications, provide insight into the initiation of this autoimmune response and identify potential therapeutic targets. The Oklahoma Clinical Immunology Serum Repository (Oklahoma City, OK, USA) contains more than 120 000 coded samples from 70 000 individuals. Sixty-eight samples from patients that tested positive for p-ANCA, and had adequate sera stored within the repository, were obtained for further analysis. Frequency matched healthy controls were selected to run in parallel experiments. This work was conducted with appropriate Institutional Review Board approval from the Oklahoma Medical Research Foundation and the University of Oklahoma Health Sciences Center (OUHSC). Patient LY294002 molecular weight sera were tested for ANCA using indirect immunofluorescence (IIF) following the protocol provided by the manufacturer (Inova Diagnostics, Inc., San Diego, CA, USA). Patient samples with a positive p-ANCA Daporinad price titre by IIF were also tested for MPO antibodies by enzyme-linked immunosorbent assay (ELISA) from the same manufacturer to verify the presence of antibodies to myeloperoxidase. The published sequence of MPO (Accession number: PO5164) was used to construct 369 decapeptides of the 745 amino acid protein overlapping by eight amino acids. The peptides were synthesized on the ends of

polyethylene pins using f-moc side-chain protection chemistry and arranged in the format of 96-well microtitre plates (Chiron Mimotopes Pty Ltd, Ketotifen Clayton, Victoria, Australia), as described previously [8,9]. Positive control peptides were synthesized on each plate using a peptide with known positive reactivity by a patient serum

sample. Solid-phase peptides were then tested for antibody reactivity using a modified enzyme-linked immunosorbent assay (ELISA) procedure described previously in detail [8,9]. Assay steps were executed by lowering the pins into microtitre plate wells and incubations were carried out in sealed plastic containers. The peptides were blocked in a 3% low-fat milk phosphate-buffered saline (PBS) solution and then incubated with sera containing primary antibodies. The solid-phase supports were washed with PBS with 0·05% Tween and then incubated with anti-human immunoglobulin (Ig)G as a secondary antibody (Jackson Immunoresearch Laboratories, West Grove, PA, USA). Following another wash period, the peptides were incubated in a para-nitrophenyl phosphate solution in order to induce a colour change if an antibody–peptide interaction was present. The colour change was measured using a micro-ELISA plate reader (Dynex Technologies, Chantilly, VA, USA) at 410 nm and the absorbance values were recorded. Positive controls were developed and normalized to an optical density (OD) of 1·0 to standardize results across plates and assays.