Crayfish IMD responds rapidly to WSSV infection and the activated IMD–Relish–AMPs pathway inhibits viral replication

One of the key innate immune pathways in invertebrates is the immune deficiency (IMD) signaling pathway, which effectively combats Gram-negative bacterial infections. In insects, the IMD pathway is involved in the defense against certain viral infections. However, the functional role of the IMD pathway in antiviral immunity remains incompletely characterized in crustaceans. Through this research, a novel IMD gene named PcIMD was characterized in Procambarus clarkii. PcIMD mRNA was abundantly expressed in hemocytes, intestine, and gills. Following stimulation with white spot syndrome virus (WSSV), transcriptional levels of PcIMD exhibited an increase in hemocytes and the intestine. Knockdown of PcIMD resulted in an upregulation of vp28 expression and increase in viral copy number. Moreover, knockdown of PcIMD reduced the animal survival during WSSV infection. The injection of a recombinant IMD protein (rPcIMD) and WSSV mixture downregulated vp28 expression and reduced the viral copy number. Furthermore, interference or overexpression of PcIMD respectively inhibited and promoted the transcript level of PcRelish and expression of antimicrobial peptides (AMPs) after WSSV stimulation. The expressions levels of AMPs were significantly downregulated after silencing of the PcRelish gene when challenged with WSSV. The up-regulation of AMPs were restored after knockdown of PcRelish and overexpression of PcIMD during WSSV infection. In addition, knockdown of PcRelish promoted vp28 expression and WSSV replication. In summary, the aforementioned results demonstrated that WSSV stimulation activated the IMD in crayfish, and its activation promoted Relish nuclear translocation, which further induced the expression of AMPs and inhibited virus replication. Our study is a valuable addition to the systematic elucidation of the response of the antiviral effects of the IMD pathway and its response to WSSV stimulation in crustaceans.