Edwardsiella virulence protein P modulates immune response and cell death in Japanese medaka, Oryzias latipes

초록

Edwardsiellosis, caused by Edwardsiella piscicida, leads to major losses in global aquaculture, and understanding its infection mechanisms is critical for effective disease control. The type VI secretion system (T6SS) effector Edwardsiella virulence protein P (EvpP) is a key virulence factor that inhibits inflammasome assembly and suppresses pyroptosis in mice; however, its role in fish pyroptosis responses remains unclear. In this study, EvpP function was explored in Japanese medaka (Oryzias latipes) using an EvpP deletion strain (Delta evpP) and a wild-type (WT) strain. Fluorescence imaging and quantitative real-time PCR (qPCR) showed that early intestinal colonization occurred in both groups, whereas bacterial loads in the kidney, liver, and posterior intestine were significantly lower in the Delta evpP-infected group at later time points (3 days post-infection, dpi). Immune-related gene (il1b and mcp1b) expression was significantly upregulated during Delta evpP infection. Flow cytometry with propidium iodide (PI) staining indicated increased cell death in the Delta evpP-infected group at 1 dpi, whereas the WT-infected group showed greater levels at 3 dpi. At 1 dpi, kidney macrophages and neutrophils showed significant between-group differences in cell death. These temporal differences indicate that EvpP delays early host cell death, consistent with the suppression of inflammasome-associated responses during the initial stage of infection. These findings were achieved using a Japanese medaka teleost model relevant to marine fish for the first time and suggest that mechanisms related to the inflammasome-associated responses observed in mice are also likely present in fish.

키워드