Immune-related genes expression and phagocytosis against White Spot Syndrome Virus after oral delivery of VP28 using Bacillus subtilis as vehicles in Litopenaeus vannamei

The regulation of immune-related genes expression and phagocytosis of White Spot Syndrome Virus (WSSV) were evaluated by oral delivery of VP28 using Bacillus subtilis as vehicles in Litopenaeus vannamei. In our initial experiment, by oral delivery of B. subtilis spores harboring VP28 (B. subtilis-VP28) to L. vannamei, the extremely high survival (Relative Percent Survival:83.3%) upon challenge with WSSV can be observed. The differences of genes expression levels of proPO, Peroxinectin (PE) and lipopolysaccharide- and beta-1, 3-glucan-binding protein (LGBP) were demonstrated among experimental groups of B. subtilis-VP28 bacterial spores, B. subtilis-VP28 supernatants, B. subtilis and control. The result showed that immune-related genes (proPO, PE and LGBP) were significantly (P0.05) upregulated in both B. subtilis-VP28 bacterial spores and B. subtilis feeding groups compared to B. subtilis-VP28 supernatants and the control groups. The phagocytosis in groups of B. subtilis-VP28 bacterial spores and B. subtilis-VP28 supernatants were enhanced significantly (P0.05). Besides, the percentage of haemocytes phagocytosing WSSV (46.83.9) in shrimp previously fed with B. subtilis-VP28 was significantly higher (P0.001) than that of phagocytosing TSV (an unrelated virus of shrimp) (14.92.2). This suggests that the heightened phagocytic activity, and thus the high-level survival of shrimp after B. subtilis-VP28 vaccination' are selective or specific towards WSSV. These results may raise the application prospective of this recombinant B. subtilis spores against WSSV infection in shrimp farms.