Utilizing NF-κB Signaling in Porcine Epithelial Cells to Identify a Plant-Based Additive for the Development of a Porcine Epidemic Diarrhea Virus Vaccine

The nuclear factor-kappa B (NF-κB) signaling pathway plays a crucial role in regulating immune responses in epithelial cells. In this study, we established a porcine epithelial NF-κB reporter cell line (PK15-KBR) as an in vitro platform to screen plant-based extracts for their potential use as vaccine adjuvants against porcine epidemic diarrhea virus (PEDV). The NF-κB inducers were further tested for toxicity assessments, either using CCK-8 assays or intramuscular injection in mice, finally followed by vaccination studies to evaluate their adjuvancy. Initial experiments confirmed that TNF-α effectively activated NF-κB signaling in PK15-KBR cells in a dose-dependent manner, validating the platform's reliability at Z' value of 0.68. Of the 224 testers, 3 candidates, including chamomile, mulberry and <i>Boerhaavia diffusa</i>, showed induction activity; however, only chamomile induced a dose-dependent response in PK15-KBR cells. As a proof of concept, chamomile, used as an adjuvant in oral vaccination, demonstrated significantly higher IgG levels at an early stage (day 14, <i>p</i> < 0.05) and enhanced IgA titers. These findings highlight the use of the PK15-KBR cell line in identifying mucosal adjuvants and position chamomile extract as a promising candidate for enhancing vaccine-induced immunity.