Protection by toxoid-induced antibody of gnotobiotic piglets challenged with the dermonecrotic toxin of Pasteurella multocida

Cellular and molecular action of the mitogenic protein-deamidating toxin from Pasteurella multocida

The mitogenic toxin from Pasteurella multocida (PMT) is a member of the dermonecrotic toxin family, which includes toxins from Bordetella, Escherichia coli and Yersinia. Members of the dermonecrotic toxin family modulate G-protein targets in host cells through selective deamidation and/or transglutamination of a critical active site Gln residue in the G-protein target, which results in the activation of intrinsic GTPase activity. Structural and biochemical data point to the uniqueness of PMT among these toxins in its structure and action. Whereas the other dermonecrotic toxins act on small Rho GTPases, PMT acts on the α subunits of heterotrimeric G(q) -, G(i) - and G(12/13) -protein families. To date, experimental evidence supports a model in which PMT potently stimulates various mitogenic and survival pathways through the activation of G(q) and G(12/13) signaling, ultimately leading to cellular proliferation, whilst strongly inhibiting pathways involved in cellular differentiation through the activation of G(i) signaling. The resulting cellular outcomes account for the global physiological effects observed during infection with toxinogenic P. multocida, and hint at potential long-term sequelae that may result from PMT exposure.

Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay (ELISA) using Recombinant Toxin for Detection of Antibodies against Pasteurella multocida Toxin

To facilitate the control of progressive atrophic rhinitis (PAR) of swine caused by toxigenic Pasteurella multocida, an enzyme-linked immunosorbent assay (ELISA) and a serum neutralization test (NT) have recently been developed to detect antibodies against the P. multocida dermonecrotic toxin (PmDNT). However, the NT is a cumbersome and time-consuming technique. To overcome these drawbacks, we developed an indirect ELISA, using recombinant PmDNT expressed in Escherichia coli, for the detection of antibodies to PmDNT in serum samples from pigs. The practical usefulness of this ELISA was compared with the NT using serum samples obtained from experimentally infected and naturally infected pigs. In the pigs experimentally inoculated with vaccine including PmDNT toxoid, the ELISA and neutralization antibodies were detected at almost the same time, and a good correlation was demonstrated between both tests (P<0.01, R(2)=0.807). Therefore, the ELISA can be used to evaluate the immune reaction of pigs after vaccination with P. multocida toxoid. In a survey conducted on a field herd with a history of clinical AR, the seropositivity by ELISA in pigs of age 4.5-6 months was increased even though the NT was negative, and the correlation was low between the results obtained with the two tests (P<0.01, R(2)=0.38). Therefore, the results indicated that this ELISA might be a useful alternative to the NT currently used to detect the antibody to PmDNT after vaccination or infection with P. multocida.

Characterization of the immunogenicity of formaldehyde detoxified Pasteurella multocida toxin

The immunogenicity of the Pasteurella multocida toxin (PMT) was studied in murine model systems. Mice were vaccinated with either formaldehyde treated pure PMT (pure toxoid) or formaldehyde treated crude extract of toxigenic P. multocida (crude toxoid). The corresponding mean anti-PMT titres, sero-conversion rates and survival rates after challenge with affinity purified PMT were compared. When assessed both by anti-PMT titres and seroconversion and challenge, pure toxoid was a more potent immunogen than crude toxoid. This greater immunogenic potency was unaffected by the addition of killed cell preparations of Bordetella bronchiseptica, non-toxigenic P. multocida and B. pertussis. Increasing anti-PMT titres and seroconversion rates were induced by increasing doses of formaldehyde treated PMT (fPMT) in the pure toxoid vaccines, but not in the vaccines containing crude toxoid. However, improved survival rates were observed for both types of vaccine, when the fPMT content was raised. Immunization of pregnant mice with vaccines containing fPMT induced protection of the offspring against challenge with PMT; the protection of the offspring corresponded to that of the mother.