| Summary: | Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of illness and death in
neonatal and recently weaned pigs. The immune protection of the piglets derives from maternal
colostrum, since this species does not receive maternal antibodies through the placenta. In the
present study, outer membrane vesicles (OMVs) obtained from main ETEC strains involved in
piglet infection (F4 and F18 serotypes), encapsulated into zein nanoparticles coated with Gantrez®®
AN-mannosamine conjugate, were used to orally immunize mice and pregnant sows. Loaded
nanoparticles were homogeneous and spherical in a shape, with a size of 220–280 nm. The diffusion of
nanoparticles through porcine intestinal mucus barrier was assessed by a Multiple Particle Tracking
technique, showing that these particles were able to diffuse efficiently (1.3% diffusion coefficient),
validating their oral use. BALB/c mice were either orally immunized with free OMVs or encapsulated
into nanoparticles (100 µg OMVs/mouse). Results indicated that a single dose of loaded nanoparticles
was able to elicit higher levels of serum specific IgG1, IgG2a and IgA, as well as intestinal IgA, with
respect to the free antigens. In addition, nanoparticles induced an increase in levels of IL-2, IL-4 and
IFN-γ with respect to the administration of free OMVs. Orally immunized pregnant sows with the
same formulation elicited colostrum-, serum- (IgG, IgA or IgM) and fecal- (IgA) specific antibodies
and, what is most relevant, offspring suckling piglets presented specific IgG in serum. Further studies
are needed to determine the infection protective capacity of this new oral subunit vaccine
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