Establishment and application of a novel tilapia head kidney cell line (THK-03) as an in vitro aquatic toxicology model: Evaluating heavy metal immunotoxicity and virus responses.

The head kidney, a primary immune organ in teleosts, serves as a critical source for immunocompetent in vitro models. Here, we established THK-03, a continuous cell line derived from the head kidney of Nile tilapia (Oreochromis niloticus), and systematically evaluated its applicability in environmental toxicology and viral pathogenesis. THK-03 exhibited stable proliferation in L-15 medium at 25 °C, maintaining epithelial morphology for over 100 passages. Species authentication by 18S rRNA sequencing and functional validation through high transfection efficiency confirmed its reliability. The cell line mounted distinct immune responses to pathogen-associated molecular patterns (PAMPs), with LPS activating both MyD88 and TRIF pathways, LTA triggering TLR2-MyD88 signaling, and poly(I:C) inducing antiviral states. In heavy metal exposure assays, chromium displayed the highest cytotoxicity, while zinc uniquely upregulated anti-inflammatory IL-10 expression. Furthermore, THK-03 supported productive replication of Singapore grouper iridovirus (SGIV), demonstrating cytopathic effects and viral particle formation. As a robust in vitro platform, THK-03 provides novel insights into immune-toxicological interactions and host-pathogen dynamics, offering broad utility for aquaculture health research.