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

Vaccination is a tool to control <i>Lawsonia intracellularis</i> (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 <i>Brachyspira hyodysenteriae</i> (Bhyo) on the immune response. The study included eighty pigs and five study groups: V-CO (LI-vaccinated and co-infected with LI + Bhyo, <i>n</i> = 21), P-CO (placebo and co-infected with LI + Bhyo, <i>n</i> = 18), V-LI (LI-vaccinated and infected with LI, <i>n</i> = 21), P-LI (placebo and infected with LI, <i>n</i> = 12), and NC (negative control, placebo and non-challenged, <i>n</i> = 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.