Molecular characterization and preliminary functional analysis of the NLRP3 inflammasome in golden pompano (Trachinotus ovatus) in response to Streptococcus agalactiae infection.

Golden pompano (Trachinotus ovatus) is an economically important marine fish in southern China, but intensive aquaculture has increased the risk of bacterial diseases, especially streptococcosis caused by Streptococcus agalactiae. As a key component of innate immunity, the NLRP3 inflammasome (NOD-like receptor family, pyrin domain containing 3 inflammasome) regulates inflammatory responses through caspase-1 (Cysteine-aspartic acid protease 1) activation and the maturation of IL-1β (Interleukin-1β) and IL-18 (Interleukin-18). In this study, five core genes associated with the NLRP3 inflammasome pathway in T. ovatus including ToNLRP3, ToASC, ToCaspase-1, ToIL-1β, and ToIL-18 were cloned and characterized. Sequence analysis showed that these genes contain conserved functional domains and share evolutionary conservation with teleost homologs. Tissue distribution analysis revealed broad expression, with relatively high levels in immune-related and mucosal tissues, including the spleen, head kidney, gill, intestine, and skin. After S. agalactiae challenge, all five genes showed inducible and tissue-dependent expression patterns, supporting their involvement in the antibacterial immune response. Fluorescence-based assays showed that ToNLRP3 was mainly localized in the cytoplasm and that ToASC interacted with ToCaspase-1, indicating the potential for inflammasome-like complex assembly. These findings provide a basis for understanding inflammasome-related immunity in golden pompano.