Detalle de: Exclusion of IgD‐, IgT‐ and IgM‐positive immune cells in Ichthyophonus ‐induced granulomas in rainbow trout Oncorhynchus mykiss (Walbaum)

Ichthyophonus (Plehn & Mulsow) is a protistan fish parasite with a broad host range (Ragan et al. 1996). It infects marine and freshwater fish species worldwide and produces a granulomatous systemic disease in vascularized organs such as heart, liver and kidney (Spanggaard et al. 1994; McVicar 1999). The susceptibility of various fish species is considerably variable. Atlantic herring (Clupea harengus L.) are highly susceptible (Rahimian & Thulin 1996), while rainbow trout Oncorhynchus mykiss (Walbaum) show a medium level of susceptibility and catfish (Ameiurus nebulosus Lesueur) are relatively resistant to this parasite (McVicar 1982, 1999). The main characteristics of the infection are multinucleated spherical parasite cells with a double wall and the tissue around the parasite contains inflammatory cells early in the infection, whereas fibrous tissue dominates late in the infection (McVicar & Maclay 1985; Franco‐Sierra & Alvarez‐Pellitero 1999; McVicar 1999). Despite the numerous histopathological studies conducted, we have no information about specific lymphocytes involved with Ichthyophonus in rainbow trout. In teleost fish, different B lymphocyte subsets can be found defined by their expression of immunoglobulin types (Igs) present in fish.