Molecular characterization and expression analysis of B cell activating factor from rock bream (Oplegnathus fasciatus)

•BAFF homolog was identified from rock bream (RbBAFF).•rRbBAFF protein was enhanced the survival and proliferation of rock bream lymphocytes.•rRbBAFF protein was upregulated the RbIL-10 and RbNFκB-1 gene expression in rock bream lymphocytes.•Higher levels of RbBAFF transcripts were detected mainly in lymphatic organs.•Transcriptional level of RbBAFF was modulated by bacterial and viral exposure.

B cell activating factor (BAFF) is a member of the tumor necrosis factor (TNF) ligand family. BAFF has been shown to induce survival and proliferation of lymphocytes. We characterized the gene encoding BAFF (RbBAFF) in rock bream (Oplegnathus fasciatus), and attempted to determine its biological functions upon immune responses. In silico analysis of RbBAFF demonstrated the presence of common TNF ligand family features, including a TNF domain, a D-E loop, and three cysteine residues that are crucial for trimer formation. Amino acid sequence alignment confirmed that RbBAFF and its homologs were conserved at secondary and tertiary levels. Transcriptional analysis indicated that RbBAFF mRNAs were ubiquitously expressed in wide array of tissues. The higher levels of constitutive expression were observed in the kidney, head kidney and spleen, suggesting an important physiological relationship with lymphocytes. Under pathological conditions, RbBAFF mRNA levels were significantly elevated. The role of RbBAFF in lymphocyte survival and proliferation was confirmed by MTT assays and flow cytometry. Recombinant RbBAFF protein (10 μg/mL) was able to prolong the survival and/or enhance the proliferation of rock bream lymphocytes by approximately 30%. Transcription of IL-10 and NFκB-1 was significantly stimulated by RbBAFF. Our findings provide further information regarding fish BAFF gene and its role in adaptive immunity.