Immune activation by Ziziphus jujuba in Galleria mellonella : challenge-specific and temporal dynamics of humoral immune responses

Abstract The immunomodulatory effects of Ziziphus jujuba Mill. fruit extracts were investigated using Galleria mellonella as an insect immune model. The expression of antimicrobial peptides, hemolin, phenoloxidase genes (PO-I and PO-II), and enzyme activity was measured in response to Candida albicans , silica beads, and Z. jujuba fruit extract. Responses were found to be stimulus- and time-dependent. Gallerimycin and galiomycin, key antimicrobial peptides, exhibited distinct expression patterns, with gallerimycin showing a more pronounced response to pathogens and beads. The Z. jujuba extract stimulated an early but balanced immune activation, likely due to its bioactive compounds. Hemolin expression varied between larvae and haemocytes depending on the type and duration of the challenge, supporting its role in immune recognition and opsonisation. Phenoloxidase activity and gene expression were also enhanced, supporting their role in promoting melanisation processes. Docking analyses suggested that hemolin contributes to phenoloxidase activation by stabilising PO-I and interacting with the phenoloxidase-activating factor-1-like protein (PAP1). The findings suggest that Z. jujuba extract effectively modulates immune responses, promoting enhanced protection while maintaining immune balance. GC-MS analysis revealed multiple bioactive compounds potentially contributing to immune modulation. This study highlights the significant immunomodulatory effects of Z. jujuba fruit extract on the immune system of G. mellonella . The findings suggest its potential as a natural immunostimulant and warrant further investigation of the underlying molecular mechanisms and bioactive components.