Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2001
Publication Date: 1/1/2002
Citation: Xu, D., Klesius, P.H., Shelby, R.A. 2002. Cutaneous antibodies in excised skin from channel catfish, ictalurus punctatus rafinesque, immune to ichthyophthirius multifiliis. Journal of Fish Diseases. pp.45-52. Interpretive Summary: Ich is a major parasite disease of freshwater fish worldwide and caused by a protozoan Ichthyophthirius multifiliis. The disease caused high mortalities and economic loss in both farmed and ornamental fish in the tens of million dollars annually. Ich infections are difficult to control with chemicals. Currently no vaccine is available to prevent Ich. In this study, we collected the skin from Ich immune fish, which were grown in culture medium. The culture fluids were harvested at different times and used to study the effect of antibodies in culture fluids on Ich. The result of this study showed that antibodies to Ich were present and released from the skin culture of fish immune to Ich. Weakening and killing of the infective Ich are two characteristics of the antibody. This antibody appears to prevent the invasion of Ich into fish indicated that a vaccine may be successfully developed.
Technical Abstract: This study determined the effect of cutaneous antibodies to Ichthyopthirius multifiliis (Ich) development in channel catfish. Culture conditions were established to observe the attachment of theronts and development of trophonts in the excised catfish tissues. Many important events involved for the same population of theronts and trophonts can be observed continuously with this in vitro model, such as theront invasion, shape transformation, trophonts rotation, relocation, development and survival. Culture fluids from excised skin of immune fish immobilized theronts and immobility of theronts was removed after immunoabsorption. Immunofluorescent staining of theronts treated with immune culture fluid revealed strong and uniform fluorescence on the cilia and cell surface of theronts. Western blot analysis of the immune culture fluid revealed a 70 kDa band which corresponded to the molecular weight of catfish immunoglobulin heavy chain. The treatment of theronts with the immune culture fluid greatly reduced the attachment of theronts, trophont size and survival in excised tissues compared to those treated with the culture fluid from naive fish. During in-vivo invasion, fewer fish were infected and the infection density was less for fish exposed to theronts treated with immune culture fluid. Results of this study show that cutaneous antibodies against Ich were present in and released from the excised skin from Ich immune fish. The antibodies significantly reduced theront infectivity by immobilizing and weakening theronts.