Macrophage migration inhibitory factor (MIF) of golden pompano (Trachinotus ovatus) is involved in the antibacterial immune response

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine with a unique structure involved in immune regulation and inflammation. In the present study, we identified a MIF from Trachinotus ovatus (golden pompano) and analyzed its function. TroMIF shares high homology (58.26%-94.78%) with the other known MIF sequences of vertebrates. TroMIF is most closely related to large yellow croaker (Larimichthys crocea). The expression of TroMIF was most abundant in the liver and head kidney, and was significantly up-regulated after Edwardsiella tarda infection. The subcellular localization of TroMIF was mostly distributed in the cytoplasm. In vitro results revealed that the recombinant protein rTroMIF could inhibit the migration of head kidney lymphocytes (HKLs) and macrophages (HKMs) and enhance the phagocytic activity of HKMs. As a pro-inflammatory cytokine, rTroMIF could increase the expression levels of some pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), interleukin 1-beta (IL-1 beta), IL-6, IL-8, and interferon-gamma (IFN-gamma) and decrease the expression of IL-10. The rTroMIF was proved to have enzymatic redox activity in vitro. Furthermore, overexpression of TroMIF in the head kidney cell line of golden pompano could significantly enhance its ability to resist E. tarda infection from 1 h to 4 h. The knockdown of TroMIF expression induced a significant increase in the number of bacteria after E. tarda infection at 1, 2, and 4 hpi. Our results suggest that TroMIF is an essential effector of the innate immune system and plays a pivotal role in antibacterial immunity.

Automated summary

In this study, a macrophage migration inhibitory factor (TroMIF) was identified from golden pompano and its function was analyzed. TroMIF showed high similarity with other known MIF sequences and was most closely related to large yellow croaker. TroMIF was highly expressed in the liver and head kidney and its expression was up-regulated after E. tarda infection. In vitro experiments showed that rTroMIF could inhibit the migration of lymphocytes and macrophages and enhance macrophage phagocytic activity. Furthermore, rTroMIF increased the expression levels of pro-inflammatory cytokines and had enzymatic redox activity. Overexpression of TroMIF enhanced the ability to resist E. tarda infection, while knockdown of TroMIF expression increased the bacterial load. These results suggest that TroMIF plays an important role in antibacterial immunity.