Immune response of DNA vaccine against lymphocystis disease virus and expression analysis of immune-related genes after vaccination

摘要

In this study, we found that an intramuscular injection of Japanese flounder (Paralichthys olivaceus, 60–80 g in weight and 15–20 mL in length) with 5 μg of a DNA vaccine (pEGFP-N2-LCDV-cn-MCP 0.6 kb, containing lymphocystis disease virus major capsid protein gene) induced a strong immune response. Subsequent real-time polymerase chain reaction showed that the expression of immune-related genes [e.g., major histocompatibility complex (MHC) class I , MHC II , T-cell receptor (TCR), tumour necrosis factor (TNF), tumour necrosis factor receptor (TNFR), Mx, interleukin (IL)-1β, CXC and IL-8R] was significantly changed after DNA vaccination. The most remarkable alternation was the expression of MHC I and MHC II genes: MHC II reached the maximum on day 8 in different tissues, and MHC I on day 2 in the intestine and gills. The expression of TCR increased and reached a plateau in 2 days in the spleen, gills, kidney and liver after vaccination and then decreased after day 8. In contrast, the expression of TCR in the intestine increased and reached a plateau in 8 days. The expression of IL-8R reached the maximum on day 2 in different tissues and then decreased on day 8. Mx increased in the gills, kidney, spleen and liver on days 2, 8, 2 and 2, but decreased in the intestine, gills, spleen and liver on days 2, 8, 8 and 8 respectively. The TNFR expression increased in the spleen, kidney and gills on days 2, 8 and 8, but decreased in intestine, liver and gills on days 2, 8 and 8 respectively. The expression of TNF, CXC and IL-1β increased 2 and 8 days after the injection of DNA vaccine. However, the expression of TNF, CXC and IL-1β altered on days 2 and 8 with different patterns in different tissues respectively. The fish responded to the DNA vaccine by yielding a specific immunoglobulin against lymphocystis disease virus (LCDV) as observed with indirect ELISA. The DNA vaccine induced a unique humoral response, suggesting that the DNA vaccine activated both cellular and humoral defences of the specific immune system of Japanese flounder.