A WHO Reference Reagent for lupus (anti-dsDNA) antibodies: international collaborative study to evaluate a candidate preparation.

INTRODUCTION: Antibodies against double-stranded DNA (anti-dsDNA) are a specific biomarker for systemic lupus erythematosus (SLE). The first WHO International Standard (IS) for anti-dsDNA (established in 1985), which was used to assign units to diagnostic tests, was exhausted over a decade ago. METHODS: Plasma from a patient with SLE was first evaluated in 42 European laboratories. The plasma was thereafter used by the National Institute for Biological Standards and Control to prepare a candidate WHO reference preparation for lupus (anti-dsDNA) antibodies. That preparation, coded 15/174, was subjected to an international collaborative study, including 36 laboratories from 17 countries. RESULTS: The plasma mainly contained anti-dsDNA, other anti-chromatin antibodies and anti-Ku. The international collaborative study showed that the field would benefit from 15/174 as a common reference reagent improving differences in performance between different assays. However, no statistically meaningful overall potency or assay parallelism and commutability could be shown. CONCLUSION: 15/174 cannot be considered equivalent to the first IS for anti-dsDNA (Wo/80) and was established as a WHO Reference Reagent for lupus (oligo-specific) anti-dsDNA antibodies with a nominal value of 100 units/ampoule. This preparation is intended to be used to align test methods quantifying levels of anti-dsDNA antibodies.

Anti-A and anti-B activity in batches of different intravenous immunoglobulin products determined using a direct haemagglutination method.

The European Pharmacopoeia requires that manufacturers assess intravenous immunoglobulin (IVIG) products for antibodies against blood groups A and B using an indirect anti-globulin test (AGT). However, this method suffers from the disadvantage that the anti-globulin reagent may be neutralised by excess IgG and invalidate the data generated. In view of this, we have used a direct microtitre-based haemagglutination method to screen batches of IVIG products from five manufacturers for anti-A and anti-B, and compared the titres with those reported by the manufacturers. The range of reported titres varied 32-fold across the different products, whereas virtually all the direct method titres fell within a 4-fold range for each specificity. This indicated that the discrepancies in reported titres were due to inconsistencies in manufacturers' testing methodology and/or interpretation of results. Our finding that the anti-globulin reagent used to bring about agglutination of anti-A- or anti-B-sensitised erythrocytes in the AGT was neutralised by excess IgG at least down to a 1 in 8 dilution of IVIG (from 5% (w/v) IgG) casts serious doubts on the suitability of the AGT for testing high immunoglobulin concentration products.