Protective immunity against iridovirus disease in mandarin fish, induced by recombinant major capsid protein of infectious spleen and kidney necrosis virus.

Infectious spleen and kidney necrosis virus (ISKNV) is the causative agent of a disease causing high mortality and economic losses in mandarin fish, Siniperca chuatsi in China. But little information about vaccine development against ISKNV disease is available. In this study the gene encoding the major capsid protein (MCP), which is predominant structural component of the iridovirus particles, was cloned into a temperature induction prokaryotic expression vector pBV220 and a recombinant protein was detected about 50 kDa in molecular weight and accounted for 23% of total proteins of whole cell. Polyclonal antibodies were raised in rabbits against the purified protein and the reaction of the antibody was confirmed by western blotting using the purified protein and the spleen and kidney of healthy and diseased mandarin fish. The recombinant protein was renatured by dialysis and the juvenile mandarin fish were vaccinated by intraperitoneal injection with recombinant MCP emulsified with ISA 763 adjuvant at a dose of 20 μg/fish, 50 μg/fish and 100 μg/fish, respectively. Specific antibodies and lymphocyte proliferation were detected in three groups and the values of MCP50 group were higher than the other two groups. After challenge infection with ISKNV, fish of MCP50 group showed significantly greater survival than the others and the RPS was 64.3%. In conclusion, the humoral immunity and cellar immunity of mandarin fish were induced by recombinant MCP and the best immune dose was 50 μg/fish. To the best of our knowledge, this is the first time that a recombinant protein vaccine against ISKNV disease was developed in mandarin fish.