Assessment in mice of vapA–DNA vaccination against Rhodococcus equi infection

• Published in: Veterinary immunology and immunopathology Vol. 104; no. 3; pp. 215 - 225
• Main Authors: Haghighi, H.R., Prescott, J.F.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 08.04.2005
• Subjects: Actinomycetales Infections - immunology; Actinomycetales Infections - prevention & control; Actinomycetales Infections - veterinary; animal disease models; Animals; Antibodies, Bacterial - blood; antibody formation; bacterial antigens; bacterial infections; Bacterial Proteins - genetics; Bacterial Proteins - immunology; Bacterial Vaccines - genetics; Bacterial Vaccines - immunology; Bacterial Vaccines - therapeutic use; cell-mediated immunity; Cercopithecus aethiops; COS Cells; DNA vaccination; Enzyme-Linked Immunosorbent Assay - veterinary; Female; foals; horse diseases; Horse Diseases - immunology; Horse Diseases - microbiology; Horse Diseases - prevention & control; Horses; immunoglobulin G; interleukin-12; intramuscular injection; liver; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; plasmids; Plasmids - genetics; Plasmids - immunology; Rhodococcus equi; Rhodococcus equi - genetics; Rhodococcus equi - immunology; Rhodococcus equi - pathogenicity; Transfection - veterinary; vaccination; Vaccination - methods; Vaccination - veterinary; vaccine adjuvants; vaccine development; Vaccines, DNA - genetics; Vaccines, DNA - immunology; Vaccines, DNA - therapeutic use; VapA; virulence; Virulence Factors - genetics; Virulence Factors - immunology; Mice; DNA vaccination; Rhodococcus equi; VapA
• ISSN: 0165-2427; 1873-2534
• DOI: 10.1016/j.vetimm.2004.12.006

There is a need to produce a vaccine against Rhodococcus equi pneumonia in foals in which immunity against infection is largely based on a type 1, cell-mediated, immune response. The VapA protein of the virulence plasmid of R. equi is highly immunogenic. To assess the potential of vapA–DNA to produce immunity, C57BL/6 and BALB/c mice were immunized with a DNA vaccine constructed from vapA incorporated into pcDNA3.1. The plasmid construct expressed VapA in a COS-7 cell line. Intramuscular immunization of mice resulted in enhanced clearance of R. equi from the liver of intravenously challenged mice compared to non-immunized controls. This effect was more marked when pORF– IL-12, a plasmid expressing murine IL12, was included with the vaccine. Antibody developed to VapA, with an IgG2a response being more marked in mice immunized with pcDNA– vapA than in non-immunized or in mice immunized with the mixed vapA and IL-12 plasmid constructs. In conclusion, this study has shown for the first time that DNA immunization with vapA enhances the immune responses of mice against R. equi infection, that the IgG subisotype response is consistent with a type 1-based immune response, and that this can be enhanced by injection of the IL-12 gene.