Immunocytochemical studies on immunoglobulin‐containing cells in the epidermis of rainbow trout Salmo gairdneri Richardson: influence of bath vaccination*

The presence of immunoglobulin–containing cells in the epidermis of rainbow trout was traced, using post–embedding immunocytochemical techniques, in resin–embedded fragments of skin. Light microscopy observations (for which the PAP method was used)revealed the presence of immunoglobulin–containing cells in the epidermis, although no accurate identification was possible. Electron microscopy observations (employing gold–labelling) showed that, in spite of the poor preservation thought unavoidable to protect the antigenicity of the immunoglobulins, the positive cells were either lymphocyte–like cells or mucous cells. Anti– Vibrio anguillarium antibody was detected in the epidermal mucous cells of rainbow trout juveniles vaccinated by immersion, using an immunoenzymatic sandwich technique, modified for resin–embedded tissue. The possibility of the existence of a local immune system is discussed, considering the involvement of the mucous cells.