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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Lectins on the Invasion of Ichthyophthirius Theront to Channel Catfish Tissue

item Xu, Dehai
item Klesius, Phillip
item Shoemaker, Craig

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2001
Publication Date: June 20, 2001

Interpretive Summary: Ichthyophthirius multifiliis (Ich) is one of the most deadly parasites of freshwater fish and causes serious problems in intensively cultured and ornamental fish. The life cycle of the parasite include 3 stages: reproductive, infective, and parasitic. A reproductive Ich undergoes multiple division to produce 100-1000 infective Ich in each cyst. Infective eIch swim actively in water and seek fish to invade. Lectins are sugar binding proteins that bind specifically to sugar residues. Sugars have been reported to be present on the surface coat of different parasites and involved in recognition and invasion to host cells. In a previous study on the early development of Ich in channel catfish tissues, we noted that some infective Ich left catfish tissues if they did not find suitable sites to invade after initial contact with host. This indicated the surface of the Ich played an important role in host invasion. Sugar lectin interactions serve as a basis for recognition and invasion for some parasites. Little i known of the interaction between lectins and Ich. In the present study, we treated young Ich using 4 lectins and examined the effect of lectin binding to Ich on the invasion of the parasites, development and survival in excised fins of channel catfish. The results show that sugar receptors were present on the surface of Ich and the treatment of Ich with lectins reduced the invasion of Ich to the excised tissue.

Technical Abstract: This study determined the effects of lectin binding to theronts of Ichthyophthirius multifiliis on theront immobilization, invasion, trophont development and survival in channel catfish (Ictalurus punctatus) excised fins in vitro. Soybean agglutinin (SBA), lentin agglutinin (LCA), gorse agglutinin (UEA-I), and wheat germ agglutinin (WGA) were used to treat theronts. Percentages of theronts immobilized by 4 lectins ranged from 12.0% to 19.4% at a concentration of 1000 g/ml. These lectins bound more than half of the theronts at a concentration of 50 g/ml. Theronts labeled by SBA and WGA were more than those labeled by lectin LCA at a concen- tration of 50 and 100 g/ml respectively. The binding of these lectins to theronts indicated that monosaccharides; D-galactose, L-fucose, D-mannose or D-glucose and amino sugar derivatives; N-acetylgalactosamine and N- acetylglucosamine were present on surface of theronts. Invasion was reduced dsignificantly for theronts treated with LCA, UEA-I, and WGA. No difference in invasion was found between controls with SBA bound theronts (P > 0.05). The binding of lectin LCA, UEA-I and WGA to theronts significantly reduced the development of trophonts (P > 0.05). The mean volumes of trophonts labeled with these 3 lectins were smaller than volumes in control trophonts from 8 to 48 h post exposure (PE). Survival was lower in trophonts labeled with lectins compared to control trophonts at 48 h PE.

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