Evaluation of immune efficacy of Omp2 protein against Lawsonia intracellularis in mice

Porcine proliferative enteropathy (PPE) is caused by the obligate intracellular bacterium Lawsonia intracellularis. Infection results in an enteric disease characterised by decreased growth performance of pigs, and presents a major economic burden for swine industries worldwide. Since vaccination is an effective technique for controlling PPE, novel effective vaccine platforms are need to be developed. In this study, five proteins of L. intracellularis were screened through animal experiments and the highly immunoprotective Omp2 protein was identified. Then, the immune efficacy of Omp2 was further evaluated based on humoral and cell mediated immune (CMI) responses, faecal bacterial shedding, histopathological lesions, immune barrier function of intestinal mucosa as well as digestive and absorptive capacity following challenge of mice with L. intracellularis. Mice immunised with Omp2 had reduced faecal shedding, fewer histopathological lesions and reduced bacteria colonisation of the ileum. Additionally, Omp2 immunised mice showed stronger serum IgG and IFN-γ levels, up-regulated Occludin and zonula occludens-1 (ZO-1) mRNA levels, as well as increased numbers of intestinal intraepithelial lymphocytes (IELs) and levels of sIgA. On the contrary, the activities of LPS, α-AMS and AKP were significantly increased. Our investigation indicated that immunization with Omp2 reduced the severity of clinical signs and provided efficacious immunoprotection for target animals against L. intracellularis infection in mouse model.