Morphological and Ultrastructural Study of Vaccine-induced Granuloma in Atlantic Salmon (Salmo salar)

Aim:  The aims of this study were immunhistochemical (IHC) and ultrastruktural characterization of cells involved in vaccine granuloma formation in Atlantic salmon. Methods:  Fish suffering from severe reaction 6 to 9 months after vaccination were selected. We investigated granuloma from peritoneum, at the injection site. Morphological staining techniques, IHC to visualise MHC+ cells and ultrastructural analysis were performed. Results:  Microbial investigations revealed no infective agents. Histological and ultrastructural studies revealed Russel bodies, macrophages, multinucleated giant cells, melanomacrophages (MMP), mast cells (MC) and Splendore–Hoepply material in the lesions. Conclusion:  Signet ring cells identified after vaccination have been hitherto described as svollen mast cells. This study shows that these cells fit the Russel body characteristic, consistent with humoral stimulation following vaccination and foreign material precipitate, Splendore-Hoepply material. MHC+ cells were located circumferal to granuloma centers. MMP were present containing melanosomes in different developmental stages.