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Updated: Aug 17, 2026
Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens
Published on: May 19, 2020
An immuno-diffusion assay to assess the protective antigen content of anthrax vaccine
Trudy Adams1, Sancha Osborn, Sjoerd Rijpkema
1Division of Bacteriology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar EN6 3QG, UK.
Abstract:
The UK anthrax vaccine uses the culture supernatant of toxigenic non-encapsulated Bacillus anthracis as a crude source for protective antigen (PA). The precise amount of PA is not known. We developed a single radial immuno-diffusion (SRD) assay and an indirect ELISA to measure PA in desorbed anthrax vaccines. Based on 23 batches, the PA contents varied from 19.1 to 88.8 microgml(-1), with an average of 39.6 microgml(-1). Analysis of four batches by ELISA revealed considerably lower levels of PA. This discrepancy can be explained by competition of other proteins for binding sites, which results in an artificially low amount of bound PA per well. We conclude that the SRD assay is a reproducible method for the measurement of PA and this assay will contribute to quality control and improve the specifications of current anthrax vaccines.
