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Diseases of Aquatic Organisms

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DAO 33:19-24 (1998)  -  doi:10.3354/dao033019

In vivo modulation of innate resistance to Edwardsiella ictaluri with a phosphatase inhibitor

Donald L. Evans1,*, Emmett B. Shotts2, Liliana Jaso-Friedmann1

1Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602, USA
2National Fish Health Laboratory, Kearneysville, West Virginia 25430, USA

Catfish were treated with the protein phosphatase inhibitor sodium orthovanadate (vanadate) and challenged with the pathogen Edwardsiella ictaluri to investigate the relationship between the in vivo immunoregulatory effects of tyrosine and serine phosphatases on nonspecific modulation of resistance to bacterial infections. Two different infection protocols were used: fish were pretreated by immersion in vanadate and subsequently infected (by immersion) with 1 LD100E. ictaluri, or fish were injected (intraperitoneally, IP) with bacteria and simultaneously treated (by immersion) with 25 µM vanadate. In the absence of vanadate, both infection models produced fulminant infection by 10 or 6 d, respectively. Zero to 48 h treatment with vanadate (by immersion) prior to infection produced 17 to 100% survival of infected fish. In addition to augmentation of innate immunity, vanadate enhanced acquired immunity to this pathogen. Fish which had vanadate-induced resistance to primary infection were 'immune' to secondary challenge with a LD100 of E. ictaluri. Experiments were done to determine the mechanism(s) of the altered innate resistance. Catfish were injected (IP) with E. ictaluri and simultaneously treated (by immersion) with 25 µM vanadate. Assays were done to measure nonspecific cytotoxic cell (NCC) activity at 0, 24, 48, 72 and 96 h post-infection/vanadate treatment. Increased NCC activity at 48 to 96 h post-infection appeared to correlate with resistance to bacterial related mortality. These data indicated that in vivo vanadate treatment of catfish significantly increased resistance to otherwise fulminant E. ictaluri infections. This effect coincided with the initiation of resistance to secondary infections without additional vanadate treatments. Vanadate-modulated resistance in catfish may be associated with augmented NCC activity.

Phosphatases · Phosphatase inhibitors · Edwardsiella ictaluri · Nonspecific cytotoxic cells · Innate immunity · Cytotoxicity · Sodium orthovanadate

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