Beta-Defensin1 from Ctenopharyngodon idella exerts immunomodulatory effects through CiHsp70-mediated antigen processing and presentation pathway activation

Beta-Defensin1 from Ctenopharyngodon idella (CiBD1) is an important antimicrobial peptide in the defensin family, which possesses a high antibacterial activity. But its immunomodulatory effects and mechanisms are still poorly understood. Here, transcription levels of the immune-related genes in the immune-related tissues, and phagocytosis and respiratory burst activities of C. idella head kidney macrophages after CiBD1 overexpression were firstly detected. The results showed that CiBD1 overexpression could significantly up-regulate transcription levels of all the tested genes in the immune-related tissues, and enhance phagocytosis and respiratory burst activity of head kidney macrophages, implying CiBD1 has immunomodulatory effects on C. idella. Subsequently, the comparative transcriptome of C. idella spleen tissues before and after CiBD1 overexpression were investigated by RNA-seq. And a total of 379 differentially expressed genes (DEGs), including 218 up-regulated and 161 down-regulated genes, were obtained between PBS-vs-overexpession group. KEGG pathway enrichment analysis showed that 105 out of 151 immune-related DEGs significantly enriched 13 immune-related pathways. Notably, the up-regulated CiHsp70 gene significantly enriched in Antigen Processing and Presentation (APP) pathway. Further, the head kidney macrophages of C. idella were used as APCs to investigate deeply whether CiHsp70 participated in the APP pathway activation by overexpression and RNAi techniques. It was found that Cihsp70 overexpression could significantly promote transcription and expression of the genes for key signaling molecules involved in APP pathway and down-stream immune effector factors, whereas Cihsp70 RNAi demonstrated opposite effects. Collectively, these findings provide a new insight into the mechanism by which CiBD1 exerts immunomodulatory effects by Hsp70-mediated APP pathway activation.