# Immune Response of Pigs Vaccinated Against Proliferative Enteropathy and Co-Infected with Lawsonia intracellularis and Brachyspira hyodysenteriae

## TL;DR

This study shows that vaccinating pigs against a gut infection helps reduce disease severity even when they are infected with another bacteria.

## Contribution

The study identifies immune responses in vaccinated pigs co-infected with two pathogens, offering new insights into protective immunity.

## Key findings

- Vaccinated pigs showed reduced intestinal lesions and bacterial shedding even with co-infection.
- Vaccination triggered stronger immune responses, including increased IgG and IFN-γ production.
- B cells appear important in local immunity, while T regulatory cells had no significant role.

## Abstract

Lawsonia intracellularis is a bacterium that causes intestinal disease in pigs, leading to poor growth and economic losses. Vaccination is one of the main ways to control this infection, but pigs are often exposed to other pathogens such as Brachyspira hyodysenteriae, which can worsen the disease. In this study, we evaluated how the immune system of pigs reacts to a vaccine made from inactivated L. intracellularis and how co-infection with B. hyodysenteriae affects this response. We examined several aspects of the pigs’ health, including intestinal lesions, presence of bacteria in the feces, and immune activity in the blood and intestine. The vaccinated pigs had fewer intestinal lesions, lower bacterial shedding, and stronger immune reactions than unvaccinated animals, even when exposed to both bacteria. These findings show that vaccination helps pigs fight against L. intracellularis infection and remain healthier, and they also provide new insights into how the immune system protects the gut. This information can help scientists and veterinarians develop better strategies to control intestinal diseases in pig production.

Vaccination is a tool to control Lawsonia intracellularis (LI) in pigs. However, pigs may have co-infections that worsen clinical signs and lesions. The aim of this study was to characterize systemic and gut-mediated humoral and cell-mediated immune (CMI) responses in pigs vaccinated with a killed intramuscular LI vaccine and to analyze the impact of co-infection with Brachyspira hyodysenteriae (Bhyo) on the immune response. The study included eighty pigs and five study groups: V-CO (LI-vaccinated and co-infected with LI + Bhyo, n = 21), P-CO (placebo and co-infected with LI + Bhyo, n = 18), V-LI (LI-vaccinated and infected with LI, n = 21), P-LI (placebo and infected with LI, n = 12), and NC (negative control, placebo and non-challenged, n = 8). Parameters analyzed: fecal score and pathogen shedding), gross intestinal lesions, LI intestinal colonization (IHC), serum IgG, LI-specific IFN-γ production (ELISPOT), and immune cell subsets (flow cytometry) in blood, mesenteric lymph nodes, Peyer’s patches, and intestinal epithelium. LI vaccination significantly reduced LI fecal shedding, intestinal colonization, and macroscopic lesions—even under Bhyo co-infection. Vaccinated pigs had earlier and stronger serum IgG and IFN-γ responses. B cells seem to play an important role in the local immune response, and T regulatory cells apparently do not have a significant role in immunomodulation. This study contributes to a better understanding of LI immune response and can provide subtract for further research in the control of LI.