Abstract
Mucosal vaccination has been demonstrated to be an effective means of eliciting protective immunity against aerosol infections of foot and mouth disease virus (FMDV) and various approaches have been used to improve mucosal response to this pathogen. In this study, cationic PLGA (poly(lactide-co-glycolide)) nano/microparticles were used as an intranasal delivery vehicle as a means administering FMDV DNA vaccine encoding the FMDV capsid protein and the bovine IL-6 gene as a means of enhancing mucosal and systemic immune responses in animals. Three eukaryotic expression plasmids with or without bovine IL-6 gene (pc-P12A3C, pc-IL2AP12A3C and pc-P12AIL3C) were generated. The two latter plasmids were designed with the IL-6 gene located either before or between the P12A and 3C genes, respectively, as a means of determining if the location of the IL-6 gene affected capsid assembly and the subsequent immune response. Guinea pigs and rats were intranasally vaccinated with the respective chitosan-coated PLGA nano/microparticles-loaded FMDV DNA vaccine formulations. Animals immunized with pc-P12AIL3C (followed by animals vaccinated with pc-P12A3C and pc-IL2AP12A3C) developed the highest levels of antigen-specific serum IgG and IgA antibody responses and the highest levels of sIgA (secretory IgA) present in mucosal tissues. However, the highest levels of neutralizing antibodies were generated in pc-IL2AP12A3C-immunized animals (followed by pc-P12AIL3C- and then in pc-P12A3C-immunized animals). pc-IL2AP12A3C-immunized animals also developed stronger cell mediated immune responses (followed by pc-P12AIL3C- and pc-P12A3C-immunized animals) as evidenced by antigen-specific T-cell proliferation and expression levels of IFN-γ by both CD4+ and CD8+ splenic T cells. The percentage of animals protected against FMDV challenge following immunizations with pc-IL2AP12A3C, pc-P12AIL3C or pc-P12A3C were 3/5, 1/5 and 0/5, respectively. These data suggested that intranasal delivery of cationic PLGA nano/microparticles loaded with various FMDV DNA vaccine formulations encoding IL-6 as a molecular adjuvant enhanced protective immunity against FMDV, particularly pc-IL2AP12A3C with IL-6 gene located before P12A3C gene.
Highlights
Foot and mouth disease virus (FMDV) infections following exposure to contaminated aerosols can be prevented by neutralizing mucosal immune responses directed against FMDV antigens, suggesting that vaccines designed to elicit mucosal FMDV-specific immunity at major mucosal surfaces can interfere with viral transmission [1]
TEM analysis revealed that cells transfected with plasmid pA (Figure 2E) and pC (Figure 2F) presented with detectable empty capsid structures but cells transfected with pB did not, perhaps because P12A protein encoded by plasmid pB harboured three additional amino acids after 2A protein self-cleavage between IL-6 and P12A protein, including the amino-terminal proline of 2A protein, upstream of amino-terminal glycine of P1, according to reports [16,17]
The nanoparticlescontaining microparticles were formulated through freeze-drying the nanoparticles with mannitol added in order to embrace the virtues of both nano- and micro-scale particles, as microparticles following pC vaccination is consistent with stronger FMDV specific antibody responses(p,0.05) and stronger FMDV neutralizing antibody responses(p.0.05) compared with that following pA vaccination, suggesting that the presence of IL-6 as a vaccine component significantly contributed to the elicitation of mucosal and humoral immune responses
Summary
Foot and mouth disease virus (FMDV) infections following exposure to contaminated aerosols can be prevented by neutralizing mucosal immune responses directed against FMDV antigens, suggesting that vaccines designed to elicit mucosal FMDV-specific immunity at major mucosal surfaces can interfere with viral transmission [1]. Since protection against mucosal infection has been attributed to the production of anti-FMDV-specific IgA antibodies [2], elicitation of IgA at these surfaces has been deemed an important parameter in the development of vaccines designed to elicit protective immune responses against FMDV [3]. PLGA nanoparticles have been used to increase the concentrations of drugs crossing various biological barriers, including the blood-brain barrier, gastrointestinal and mucosal surfaces and ocular tissues [12]. Chitosan-coated PLGA nanoparticles were found to increase the penetration of the encapsulated macromolecules at mucosal surfaces [12,15]
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