Fusion with CTB enhances the immunogenicity and protective efficacy of MIC2 subunit vaccine against Eimeria tenella

Coccidiosis is a parasitic disease caused by Eimeria species in chickens, leading to substantial threats to the poultry industry worldwide. Vaccination has emerged as a pivotal preventive strategy, with subunit vaccines gaining significant attention due to their safety. Microneme protein 2 (MIC2) of Eimeria tenella (E. tenella) is a promising candidate antigen for coccidiosis vaccination. However, its immune protection efficiency still needs to be further improved. Here, we report that MIC2, cholera toxin B subunit (CTB) and their fusion protein CTB-MIC2 are successfully recombinant expressed and produced in Pichia pastoris (P. pastoris). Notably, CTB and CTB-MIC2 exhibit high affinity for GM1 ganglioside, whereas MIC2 does not. Furthermore, upon administration to mice, the fusion protein CTB-MIC2 triggered a more robust cellular and humoral immune response than MIC2 alone, as evidenced by inducing significantly higher levels of cytokines IFN-γ and IL-4, along with an elevated production of antigen-specific IgG antibodies. More importantly, CTB-MIC2 provided higher immune protection against E. tenella infections in chickens than MIC2. Taken together, these findings reveal that CTB fusion enhances the immunogenicity of MIC2, highlighting a promising strategy for developing effective anti-coccidial subunit vaccines.