Recombinant porcine rotavirus VP4 and VP4-LTB expressed in Lactobacillus casei induced mucosal and systemic antibody responses in mice

Lactobacillus casei expressing the major protective antigen VP4 of porcine rotavirus (pPG612.1-VP4) or VP4-LTB (heat-labile toxin B subunit from Echerichia coli) (pPG612.1-VP4-LTB) fusion protein was used to immunize mice orally. The expression of recombinant pPG612.1-VP4 and pPG612.1-VP4-LTB was confirmed by SDS-PAGE and Western blot analysis and surface-displayed expression on L. casei was verified by immunofluorescence. Mice orally immunized with recombinant protein-expressing L. casei produced high levels of serum immunoglobulin G (IgG) and mucosal IgA. The IgA titters from mice immunized with pPG612.1-VP4-LTB were higher than titters from pPG612.1-VP4-immunized mice. The induced antibodies demonstrated neutralizing effects on RV infection.These results demonstrated that VP4 administered in the context of an L. casei expression system is an effective method for stimulating mucosal immunity and that LTB served to further stimulate mucosal immunity suggesting that this strategy can be adapted for use in pigs.Rotaviruses are members of the family Reoviridae. Rotaviruses affecting pigs are classified as group A, B or C based on their respective inner capsid protein sequences[1]. The rotavirus double-stranded RNA genome is composed of 11 segments enclosed by a nonenveloped, triple-layered icosahedral capsid [2]. The outer capsid VP4 protein can induce neutralizing antibodies resulting in protecting herd from porcine rotavirus infection.Porcine rotaviruses are the major cause of acute diarrhea in the piglets [3,4] and can cause mild-severe diarrhea associated with potentially high morbidity and mortality. Group A rotaviruses cause diarrhea in pigs both before and after weaning [5] and can account for 53 and 44% pre- and post-weaning rotavirus-associated diarrhea in swine, respectively [6]. A recent report attributed 89% of all rotavirus-associated diarrhea in commercial pig farms to group A rotavirus infections [7]. Since rotaviruses can survive in the environment for