A simple method to quantify staphylococcal protein A in the presence of human or animal IgG in various samples

Immunoassays designed to measure low concentrations of staphylococcal prote in A (SPA) that have been leached into antibody preparations intended for t herapeutic use are subject to differing degrees of interference. Methods es tablished to quantify SPA in murine antibody preparations are not accurate in the presence of human or humanized IgG. We report the development of an enzyme-linked immunosorbent assay (ELISA) for SPA with a detection limit of 7 pg/ml and the optimization of a method that permits complete dissociatio n of SPA-immunoglobulin-complexes. This assay is a modification of our heat -mediated dissociation (HD-SD) treatment with sodium dodecyl sulfate (SDS) and diethylenetriaminepentacetic acid (DTPA) for total immune-complex disso ciation, in which the heat treatment has been prolonged and the diluent is characterized by increased protein content and buffering capacity. The dilu ent developed contains SDS, DTPA and bovine serum albumin dissolved in a 0. 1 M phosphate buffer (pH 7.2). To validate the efficiency of this novel met hod, a series of samples have been assayed, including samples reconstituted in vitro, samples of purified antibodies, and plasma from patients. The de scribed method has been shown to be generally efficient in quantitating all native and recombinant SPA in samples containing up to 50 mg/ml of human I gG. These data demonstrate the utility of this technique in determining SPA contamination of recombinant immunoglobulin therapeutic products. (C) 2000 Elsevier Science B.V. All rights reserved.