Oral vaccination with a recombinant Lactobacillus plantarum expressing the Eimeria tenella rhoptry neck 2 protein elicits protective immunity in broiler chickens infected with Eimeria tenella

Chicken coccidiosis is a protozoan disease that leads to considerable economic losses in the poultry industry. Live oocyst vaccination is currently the most effective measure for the prevention of coccidiosis. However, it provides limited protection with several drawbacks, such as poor immunological protection and potential reversion to virulence. Therefore, the development of effective and safe vaccines against chicken coccidiosis is still urgently needed. In this study, a novel oral vaccine against Eimeria tenella was developed by constructing a recombinant Lactobacillus plantarum (NC8) strain expressing the E. tenella RON2 protein. We administered recombinant L. plantarum orally at 3, 4 and 5 days of age and again at 17, 18 and 19 days of age. Meanwhile, each chick in the commercial vaccine group was immunized with 3 × 102 live oocysts of coccidia. A total of 5 × 104 sporulated oocysts of E. tenella were inoculated in each chicken at 30 days. Then, the immunoprotection effect was evaluated after E. tenella infection. The results showed that the proportion of CD4+ and CD8+ T cells, the proliferative ability of spleen lymphocytes, inflammatory cytokine levels and specific antibody titers of chicks immunized with recombinant L. plantarum were significantly increased (P < 0.05). The relative body weight gains were increased and the number of oocysts per gram (OPG) was decreased after E. tenella challenge. Moreover, the lesion scores and histopathological cecum sections showed that recombinant L. plantarum can significantly relieve pathological damage in the cecum. The ACI was 170.89 in the recombinant L. plantarum group, which was higher than the 150.14 in the commercial vaccine group. These above results indicate that L. plantarum expressing RON2 improved humoral and cellular immunity and enhanced immunoprotection against E. tenella. The protective efficacy was superior to that of vaccination with the commercial live oocyst vaccine. This study suggests that recombinant L. plantarum expressing the RON2 protein provides a promising strategy for vaccine development against coccidiosis.