Effects of infection with the ectoparasite Argulus japonicus (Thiele) and administration of cortisol on cellular proliferation and apoptosis in the epidermis of common carp, Cyprinus carpio L., skin

The host-parasite interaction between juvenile carp, Cyprinus carpio, and t he ectoparasitic branchiuran, Argulus japonicus, together with the role of cortisol in this interaction, was examined at the level of the host skin ep idermis. Epidermal mucous cell numbers, and proliferation and apoptosis of the epithelial cells were studied over 32 days. Apoptotic cell numbers in t he uppermost epidermis were reduced at 26 days post-infection with A, japon icus while the other parameters were unaffected. Administration of cortisol -containing food resulted in reduced apoptosis in the cells in the upper sk in epidermis at 24 h and at 28 days post-feeding. Cortisol feeding combined with A. japonicus infection reduced numbers of apoptotic cells in the uppe r epidermis more than either individual treatment. Further, combining the t reatments also significantly increased apoptosis in the lower epidermis in cells morphologically identified as leucocytes apparently migrating macroph ages and lymphocytes. Using immunohistochemistry, we demonstrated cortisol receptor presence and cellular localization in the teleost epidermis. Recep tors only occurred in pavement cells in the upper epidermis and in leucocyt es in the lower parts of the epidermis. The ectoparasites, or administered cortisol, induced effects which may be functionally adaptive in the upper p avement cells, while combining the two treatments also induced changes indi cative of immunosuppression.