Characterization of the immunogenicity of formaldehyde detoxified Pasteurella multocida toxin

Immunogenicity and protective efficacy of a multi-epitope recombinant toxin antigen of Pasteurella multocida against virulent challenge in mice

Pasteurella multocida (P. multocida) infection frequently results in porcine atrophic rhinitis and swine plague, leading to large economic losses for the swine industry worldwide. P. multocida toxin (PMT, 146 kDa) is a highly virulent key virulence factor that plays a vital role in causing lung and turbinate lesions. This study developed a multi-epitope recombinant antigen of PMT (rPMT) that showed excellent immunogenicity and protection in a mouse model. Using bioinformatics to analyse the dominant epitopes of PMT, we constructed and synthesized rPMT containing 10 B-cell epitopes, 8 peptides with multiple B-cell epitopes and 13 T-cell epitopes of PMT and a rpmt gene (1,974 bp) with multiple epitopes. The rPMT protein (97 kDa) was soluble and contained a GST tag protein. Immunization of mice with rPMT stimulated significantly elevated serum IgG titres and splenocyte proliferation, and serum IFN-γ and IL-12 were upregulated by 5-fold and 1.6-fold, respectively, but IL-4 was not. Furthermore, the rPMT immunization group exhibited alleviated lung tissue lesions and a significantly decreased degree of neutrophil infiltration compared with the control groups post-challenge. In the rPMT vaccination group, 57.1% (8/14) of the mice survived the challenge, similar to the bacterin HN06 group, while all the mice in the control groups succumbed to the challenge. Thus, rPMT could be a suitable candidate antigen for developing a subunit vaccine against toxigenic P. multocida infection.

Development of immunization trials against Pasteurella multocida

Pasteurellosis is one of the most important respiratory diseases facing economically valuable farm animals such as poultry, rabbit, cattle, goats and pigs. It causes severe economic loss due to its symptoms that range from primary local infection to fatal septicemia. Pasteurella multocida is the responsible pathogen for this contagious disease. Chemotherapeutic treatment of Pasteurella is expensive, lengthy, and ineffective due to the increasing antibiotics resistance of the bacterium, as well as its toxicity to human consumers. Though, biosecurity measures played a role in diminishing the spread of the pathogen, the immunization methods were always the most potent preventive measures. Since the early 1950s, several trials for constructing and formulating effective vaccines were followed. This up-to-date review classifies and documents such trials. A section is devoted to discussing each group benefits and defects.

Signaling cascades of Pasteurella multocida toxin in immune evasion

Pasteurella multocida toxin (PMT) is a protein toxin found in toxigenic strains of Pasteurella multocida. PMT is the causative agent for atrophic rhinitis in pigs, a disease characterized by loss of nasal turbinate bones due to an inhibition of osteoblast function and an increase in osteoclast activity and numbers. Apart from this, PMT acts as a strong mitogen, protects from apoptosis and has an impact on the differentiation and function of immune cells. Many signaling pathways have been elucidated, however, the effect of these signaling cascades as a means to subvert the host’s immune system are just beginning to unravel.

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.

Pasteurella multocida toxin (PMT) activates RhoGTPases, induces actin polymerization and inhibits migration of human dendritic cells, but does not influence macropinocytosis

Dendritic cells (DCs) are considered as one of the principal initiators of immune responses. In their immature state, they migrate into peripheral tissue in order to uptake antigen and to patrol for danger signals. Upon maturation, they acquire the ability to migrate to the lymph nodes and present the captured antigens to T cells in order to direct the development of specific immune responses. There is evidence that microbial compounds interfere with proper functions of DCs in order to block innate and specific immunity. Here we characterized the influence of Pasteurella multocida toxin (PMT) on monocyte-derived DCs. Using pull-down assays with recombinant rhotekin or p21-activated kinase, we demonstrated the activation of RhoGTPases by PMT in DCs. Moreover, PMT induced changes in DC morphology and actin polymerization, impaired chemotaxin-induced actin re-organization and inhibited their migration response. However, macropinocytosis was not influenced by PMT. In summary, these data indicate that PMT inhibits proper function of the motility machinery in DCs, which might limit the development of adaptive immune surveillance during infection with Pasteurella multocida.

Development of a genetically modified nontoxigenic Pasteurella multocida toxin as a candidate for use in vaccines against progressive atrophic rhinitis in pigs

OBJECTIVE

To construct a genetically modified nontoxigenic Pasteurella multocida toxin (PMT) and examine its immunoprotective activity against challenge exposure with wild-type PMT in pigs.

ANIMALS

5 healthy pigs.

PROCEDURE

A nontoxigenic PMT was created by replacing the serine at position 1164 with alanine (S1164A) and the cysteine at position 1165 with serine (C1165S). Toxic activity was determined by use of the guinea pig skin test and mouse lethality test. Three pigs were vaccinated twice with the modified PMT, and the remaining 2 pigs served as nonvaccinated control animals. Vaccinated and control pigs were challenge exposed with wild-type PMT. Pigs were euthanatized and necropsied on day 14 after challenge exposure. Turbinate atrophy was examined macroscopically and assigned a score. Serum anti-PMT antibodies were determined by use of an ELISA.

RESULTS

The genetically modified PMT was characterized by a total lack of toxic activity. Pigs vaccinated with the modified PMT became seropositive; in contrast, control pigs remained seronegative. Necropsy revealed that the 2 control pigs had moderate and severe turbinate atrophy, respectively, whereas the 3 vaccinated pigs did not have any lesions in the turbinates or abnormalities in other organs.

CONCLUSIONS AND CLINICAL RELEVANCE

Modification by use of S1164A and C1165S leads to a complete loss of toxic effects of PMT without impairment of the ability to induce protective immunity in pigs. Analysis of these results suggests that genetically modified PMT may represent a good candidate for use in developing a vaccine against progressive atrophic rhinitis in pigs.

Protective effect of Pasteurella multocida cell-free antigen and toxoid against challenge with toxigenic strains of pasteurella multocida in mice

The cell-free antigen (CFA) obtained from the culture supernatant of Pasteurella multocida (P. multocida) and the toxin (PMT) purified from CFA were inactivated and mixed with oil adjuvant to prepare a trial vaccine. Both of the mice immunized with CFA and PMT toxoid vaccine were noticeably protected against intratracheal challenge with toxigenic strains of P. multocida. Nevertheless, the protective indices of the mice immunized with CFA vaccine indicate that it is more protective and clears away the bacteria more promptly than in the mice immunized with PMT vaccine. The results suggested that CFA would possibly be good as an effective antigen to toxigenic strains of P. multocida infection.

Induction of protective immunity in rabbits by coadministration of inactivated Pasteurella multocida toxin and potassium thiocyanate extract

Pasteurella multocida is a bacterial pathogen that causes rhinitis (snuffles), pneumonia, otitis media, septicemia, metritis, and death in domestic rabbits. Currently, there are no effective vaccines to prevent infection by this organism. Subcutaneous (s.c.) immunization with either exotoxin or thiocyanate extracts of P. multocida induces partial protection in rabbits. Since disease begins at mucosal sites, induction of local immunity may be important in preventing systemic disease. Little is known concerning the efficacy of intranasal (i.n. ) administration of these antigens in inducing protective mucosal immunity to P. multocida in rabbits. The purpose of this study was twofold: (i) to investigate the effectiveness of vaccination with purified P. multocida toxin (PMT) and a potassium thiocyanate extract of P. multocida (CN) in combination and (ii) to evaluate the efficacy of administration of these antigens i.n. versus s.c. Forty-eight rabbits were randomly divided into eight different treatment groups. Rabbits received either one or both antigens by either s.c. or i.n. administration. Following vaccination, each group received an i.n. challenge of P. multocida. Rabbits vaccinated with both antigens i.n. or s.c. had a 100% survival rate, few or no bacteria in the liver and lungs, high serum immunoglobulin G (IgG) and IgM antibody titers, and significant numbers of IgG antibody-secreting cells (ASC) in the spleen and tracheobronchial lymph node. Rabbits vaccinated i.n. had significant nasal and bronchoalveolar lavage IgA antibody levels. Rabbits vaccinated with only one antigen, either PMT or CN, had lower antibody titers, moderate to severe liver and lung infections, and fewer ASC compared to rabbits receiving both antigens. Rabbits in the control groups had moderate to severe liver and lung infections. This study indicates that i.n. immunization with both PMT and CN induces an effective response against homologous P. multocida challenge.