Heat-Inactivated Selenium Nanoparticle-Enriched Lactobacillus Enhance Mucosal IgA Responses and Systemic Responses of Clostridium perfringens Multi-Epitope Vaccine Correlated with TGF-β and NF-κB Pathways in Mice

<i>Clostridium perfringens</i> is one of the main causes of death in poultry with no vaccines approved for poultry at present. The appropriate adjuvant is critical for the development of vaccines in <i>C. perfringens</i> in poultry. Here, we utilized <i>Levilactobacillus brevis</i> for high-yielding selenium biotransformation and demonstrated that heat-inactivated nano-selenium <i>Lactobacillus</i> (HiSeL) is a safe, efficient, and chemically stable selenium immunopotentiator for <i>C. perfringens</i> vaccines. We evaluated the effectiveness of HiSeL as an immune adjuvant to modulate the efficacy of multi-epitope vaccine in mice. Subcutaneous immunization mice with HiSeL promoted high levels of specific IgG, modulated cytokine secretion, downregulated stress-related gene expression, and provided 100% protection against lethal challenge with <i>C. perfringens</i>. Surprisingly, we found that HiSeL can quickly and effectively induce SIgA production even by subcutaneous immunization. Transcriptome sequencing revealed the pivotal role of TGF-β and NF-κB signaling pathways in IgA immune responses in mice immunized with the HiSeL-adjuvanted multi-epitope vaccine. Collectively, our study provides proof-of-concept evidence that HiSeL functions as a potent adjuvant candidate for the multi-epitope vaccine in a murine model, offering new insights into the development of engineered postbiotic-based adjuvants.