Detection of residual pertussis toxin in vaccines using a modified ribosylation assay

Pertussis toxin (PTx) in its detoxified form is an important component of both whole cell and acellular pertussis vaccines (ACVs). For safety reasons, it is imperative to ensure that the quantity of residual PTx in vaccines does not exceed permissible levels. The majority of the toxic effects of PTx have been attributed to the consequences of PTx-catalyzed ribosylation of the alpha-subunits of signal-transducing guanine-nucleotide-binding proteins. In this report PTx ribosylation activity was determined by an improved enzymatic-high performance liquid chromatography coupled assay using a fluorescein labeled Galpha(i3)C20 peptide. The effect of aluminum salts and other vaccine components on the assay system were also studied. The enzymatic assay system was shown to be a convenient, sensitive method and correlate well with the toxicity observed in vivo by the histamine sensitization assay. This method forms the basis of a new assay which could replace the unsatisfactory animal test currently used in pertussis vaccines control.