Immune response of orange-spotted grouper, Epinephelus coioides against Ganoderma microsporum immunomodulatory protein

Grouper is an important aquacultural fish species. This particular species has a high commercial value and is widely cultured in Southeast Asia, including in Taiwan. Viral infection can seriously impact the grouper fish industry. An effective strategy to improve grouper fish health is to increase immunity against the pathogen. GMI, an immunomodulatory protein cloned from Ganoderma microsporum, is reported to have the immunomodulatory function. In the present study, we injected and tested the influence of GMI on fish immune system in vivo by measuring the immune gene expression of GMI stimulated grouper head kidney and spleen. The GMI was injected into the Grouper using intraperitoneal injection. Post injection, we used real-time PCR to measure the immune gene expression in its head kidney and spleen. The immune related gene includes the innate immune and adaptive immune system. We observed that GMI had more influence in the spleen. Low dosage of GMI (2 ng/g of fish weight) would stimulate IRF3、IRF10、Viperin、ISG15、Mx I、Mx II、CL4、IL-1β & TNF-α expression which relates to interferon system. The fish interferon system is divided into two group: Type-I Interferon (I-IFNs) and type-II Interferon (IFN-γ). The Fish interferon system involves innate and adaptive immune systems. GMI will stimulate the fish interferon system. Mx, IFN-stimulated genes, can be divided into three isoforms. The gene expression of the profile is different from each other. Evaluated Mx isoforms have a different role in the Grouper immune system. Immunoglobulin M (IgM) is the first antibody that is produced in the immune system and provides a crucial first line of defense for the immune system.. Grouper IgM can be divided to two part, IgM heavy chain (IgM-H) and light chain (IgM-L). We observed that IgM-H and IgM-L genes were up-regulated. It would be prudent to evaluate how GMI can strengthen grouper adaptive immunity. The immune gene in grouper kidney (GK) cell with 7.5 μg /ml GMI can be stimulated to have the most expression. We examined the anti-virus ability of GMI by using GK cells treated with GMI 8 μg /ml at 12 hr then infected with grouper iridovirus (GIV) at 18 hr. The results were compared with Poly:IC. The results showed that GMI and Poly:IC can against GIV. The anti-virus capabilities of GMI was better than Poly:IC. The results show that GMI can not only stimulate the innate immune system but also the adaptive immune system as well.