Molecular characterization and immune regulatory function of Rab5a in yellow drum (Nibea albiflora) following Vibrio harveyi infection.

Rab5a is a key regulator of phagosome formation, yet its role in teleost antibacterial immunity remains largely unexplored. Here, we characterized the Rab5a gene from yellow drum (Nibea albiflora) and investigated its function in response to Vibrio harveyi infection. The open reading frame of NaRab5a is 651 bp, encoding a 216-amino acid protein highly conserved across vertebrates, with the highest identity (99.54%) to that of Collichthys lucidus. NaRab5a was constitutively expressed in all examined tissues, with the highest level in the brain. Upon V. harveyi challenge, NaRab5a transcripts were significantly up-regulated in immune-related tissues (spleen, head-kidney, liver) and the brain, and the corresponding increases in protein expression confirmed by immunohistochemistry. GST pull-down assays identified beta-actin and tropomyosin as NaRab5a-interacting proteins, suggesting a link to cytoskeletal dynamics. Critically, functional assays in RAW264.7 macrophages demonstrated that exogenous NaRab5a significantly enhanced phagocytosis, while Rab5a knockdown not only impaired phagocytic activity but also suppressed the expression of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β), iNOS, NF-κB, and IFN-γ. Collectively, these results demonstrate that Rab5a is an inducible immune molecule in yellow drum that promotes phagocytosis, likely through cytoskeletal interactions and modulation of the inflammatory cytokine network, highlighting its pivotal role in host defense against bacterial infection.