# Induction of Immune Responses in Mice and Newborn Piglets by Oral Immunization with Recombinant Lactococcus lactis Expressing S1 and M Proteins of Porcine Epidemic Diarrhea Virus

## TL;DR

This study shows that oral vaccines using modified bacteria can boost immune responses in mice and piglets against a deadly swine virus.

## Contribution

The study introduces recombinant Lactococcus lactis as a novel oral vaccine vector for inducing immune responses against PEDV.

## Key findings

- Recombinant L. lactis strains significantly stimulated lymphocyte proliferation in mice.
- The vaccine increased CD3+, CD4+, and CD8+ cell proportions in mice and piglets.
- Serum IgG, IgA, and mucosal SIgA levels were elevated in piglets after vaccination.

## Abstract

Porcine epidemic diarrhea (PED) is a severe gastrointestinal disease caused by the porcine epidemic diarrhea virus (PEDV), a virus that spreads through the intestinal tract, leading to significant economic losses in the global swine industry. Therefore, compared to traditional injection method, developing vaccines that effectively stimulate the mucosal immune system to induce a protective immune response is crucial for PED prevention. This study evaluated the immunogenicity of recombinant Lactococcus lactis (L. lactis) strains expressing the PEDV S1 and M proteins (MG1363/pMG36e-S1 and MG1363/pMG36e-M) via oral administration in BALB/c mice and neonatal piglets, assessing cellular, humoral, and mucosal immune responses in the host. The results demonstrated that the recombinant strains significantly stimulated lymphocyte proliferation in mice and increased the proportion of CD3+, CD4+, and CD3+, CD8+ double-positive cells in the spleens of mice and the peripheral blood of piglets (p < 0.05). Furthermore, the recombinant strains significantly increased serum IgG, IgA, and mucosal SIgA levels in piglets (p < 0.05). Meanwhile, serum cytokine levels, including IL-4 and IFN-γ, were significantly elevated in piglets when compared to the control group (p < 0.05). In conclusion, the recombinant L. lactis demonstrated promising potential as a novel live vector vaccine against PEDV.