Nasal vaccination with attenuated Salmonella expressing VapA: TLR2 activation is not essential for protection against R. equi infection.
Virulent strains of Rhodococcus equi have a large plasmid of 80-90kb, which encodes several virulence-associated proteins (Vap), including VapA, a lipoprotein highly associated with disease. We have previously demonstrated that oral immunisation with attenuated Salmonella enterica Typhimurium strain expressing the antigen VapA (STM VapA+) induces specific and long-term humoral and cellular immunity against R. equi. It was shown that VapA activates Toll-like receptor 2 (TLR2) on macrophages by establishing an interaction that ultimately favours immunity against R. equi infection. The purpose of this study was to evaluate the immune response triggered by nasal immunisation with STM VapA+ and to determine whether TLR2 supports the vaccine effect. We developed an optimised protocol for a single nasal immunisation that conferred protection against R. equi infection in mice, which was manifested by efficient R. equi clearance in challenged animals. Nasal vaccination with STM VapA+ has also induced protection in Tlr2(-/-) mice and mice with non-functional TLR4. Moreover, spleen cells of vaccinated mice augmented T-bet expression, as well as the production of IL-12, IFN-γ, nitric oxide and hydrogen peroxide. Notably, the population of CD4(+) T cells with memory phenotype significantly increased in the spleens of vaccinated mice challenged 1 or 5 months after immunisation. In these animals, the spleen bacterial burden was also reduced. When similar experimental procedures were performed in TLR2 knockout mice, an increase in CD4(+) T cells with memory phenotype was not observed. Consequently, we conclude that nasal vaccination with attenuated Salmonella expressing the R. equi virulence factor VapA confers long-lasting protection against experimental rhodoccocosis and that TLR2 engagement was not crucial to induce this protection but may be required for a long-term immune response.
Departamento de Biologia Celular e Molecular e Bioagentes Patogênicos, Faculdade de Medicina de Ribeirão Preto, USP, 14049-900, Brazil; Invent Biotecnologia, 14040-900, Brazil.
Silvia Almeida
SA
Cardoso
Aline Ferreira
AF
Oliveira
Luciana Pereira
LP
Ruas
Marcel Montels
MM
Trevisani
Leandro Licursi
LL
De Oliveira
Ebert Seixas
ES
Hanna
Maria Cristina
MC
Roque-Barreira
Sandro Gomes
SG
Soares
D000193:Actinomycetales Infections / Q000276:immunology / Q000517:prevention & control*; D000281:Administration, Intranasal; D000818:Animals; D058491:Bacterial Load; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology*; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D004337:Drug Carriers; D005260:Female; D005822:Genetic Vectors; D007156:Immunologic Memory; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016929:Rhodococcus equi / Q000235:genetics / Q000276:immunology*; D012486:Salmonella typhimurium / Q000235:genetics*; D013154:Spleen / Q000276:immunology / Q000382:microbiology; D013601:T-Lymphocytes / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000172:deficiency / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000172:deficiency / Q000276:immunology
D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D004337:Drug Carriers; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C541879:VapA protein, Rhodococcus equi
Attenuated Salmonella; Rhodococcus equi; Toll-like receptors; VapA; Vectored vaccine