Detection of stable epitopes on formaldehyde-detoxified Pasteurella multocida toxin by monoclonal antibodies

Progressive atrophic rhinitis in pigs can be prevented by vaccination of pregnant sows with formaldehyde-detoxified preparations of either crude extract of toxigenic Pasteurella multocida or purified P. multocida toxin (PMT). The protective value of a vaccine is expected to be related to its content of detoxified immunogenic PMT, but previously described methods for detection of PMT cannot be used for the quantification of formaldehyde-detoxified PMT. In contrast to the epitopes on PMT recognized by previously produced anti-PMT monoclonal antibodies (mAbs), two of the epitopes recognized by mAbs developed in this study showed a significant stability after treatment with formaldehyde under conditions relevant for production of vaccines. When analysed in a sandwich ELISA based on these two mAbs, the titre of a preparation of PMT, detoxified by treatment with 1% (w/v) formaldehyde for 48 h at 20 degrees C, decreased by less than 30% when compared to the titre of native PMT. A close relationship between the amount of formaldehyde-treated PMT in a vaccine determined by the sandwich ELISA and its immunogenic properties in mice was observed.