Cell-mediated response against heat-inactivated viral hemorrhagic septicemia virus (VHSV) IVb using rainbow trout (Oncorhynchus mykiss) dorsal fin cells as antigen presenting cells.

Cytotoxic T cell responses are crucial during infections and are well-characterized in mammals, however, their roles in teleost fish remain poorly understood. This study used a primary dorsal fin cell-based assay to investigate viral-antigen dependant cytotoxic responses in rainbow trout against the viral hemorrhagic septicemia virus (VHSV) IVb. The cell surface expression of the antigen presentation markers MHC-I and MHC-II were analyzed by flow cytometry in dorsal fin cells and splenocytes. Cytotoxic activity was analyzed by using dorsal fin cells stimulated with heat-inactivated viral hemorrhagic septicemia virus (VHSV) IVb and co-cultured with splenocytes from heat-inactivated VHSV-injected trout. Cytotoxic response was assessed using a lactate dehydrogenase (LDH) release assay and chaperones expression was analyzed by Western blot. Dorsal fin cells expressed both MHC-I and MHC-II showing antigen-presenting features. In addition, VHSV-stimulated fin cells co-cultured with activated splenocytes resulted in a significantly higher LDH release at 12 h compared to controls. Splenocytes from VHSV-injected fish had a higher cytotoxic response than splenocytes from naïve fish, indicating a viral-antigen dependent cytotoxic activity. To assess the role of MHC-I in this recognition, an anti-MHC-I antibody was used to block MHC-I molecules on dorsal fin cells prior to co-culture. MHC-I blockade significantly reduced LDH release, confirming the importance of MHC-I-mediated antigen presentation. These findings demonstrate that splenocytes from VHSV-injected trout exhibit greater cytotoxicity activity than naïve cells, in a manner dependent on MHC-I-mediated antigen presentation on target cells. Furthermore, dorsal fin cells are promising candidates as antigen-presenting cells and represent a valuable tool for studying antigen presentation and T cell activation in response to different pathogens or vaccine candidates.