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Passive immunization of rainbow trout with chicken immunoglobins (IGY) Arasteh, Nikoo

Abstract

Passive immunization as an alternative to vaccination or antibiotic therapy, involves use of a pathogen specific antibody raised in other animals to provide extended disease resistance to the host animals or humans. The egg yolks of hens are a rich source of specific immunoglobulins (IgY) which can be easily extracted and incorporated into the human or animal diets. However, an effective method of IgY delivery into the host animal system is needed. In this study, enhancement of rainbow trout resistance against Vibrio anguillarum infection has been used as a model to investigate passage of IgY through the gut barrier into the bloodstream and the passive immunization that pathogen specific IgY may confer. High titers of anti-V. anguillarum IgY were raised in vaccinated hens, recovered from the water-soluble fraction (WSF) of the egg-yolks and subsequently used in intraperitoneal (IP) injection, oral intubation or feeding of the trout. Western blotting of such IgY revealed a strong reactivity with V. anguillarum whole cell lysate and lipopolysaccharide, which was as strong as that of the rabbit IgG and stronger than that of the fish IgM. Immunological properties of IgY as measured by ELISA were not affected by freeze-drying, vacuum microwave drying, air-drying, or spray drying. IP injected anti- Vibrio IgY was transferred into the fish system in high enough levels to confer protection against Vibriosis in an experimental challenge. This protective effect which was retained at least 14 days post IgY injection, proved efficacy of pathogen-specific IgY in enhancement of disease resistance. To investigate absorption through trout digestive tract, IgY was intubated both anally and orally at the levels of 0.1mg and 1.4-2.7mg fish-1, respectively. Under the conditions of this study, anally intubated IgY (0.1mg) did not appear in the serum in a detectable level. Oral intubation of WSF led to absorption of IgY in an immunologically active form; however the levels were 800 to 2500 times lower than those resulting from IP injection. Among the detergents co-administered with IgY, deoxycholate, Mega9 and octyl-β-glucoside mediated the highest enhancement of IgY absorption. Use of Mega9 raised serum IgY to levels only 12 to 18 times lower than the levels after IP injection o f a similar dose. Encapsulation of WSF in polylactide-co-glycolide did not improve IgY uptake. Oral administration of anti-Vibrio IgY in co-delivery with detergents resulted in different levels of protection of rainbow trout against Vibriosis following an immersion challenge, which in some cases was comparable to the protection offered by IP injection of IgY. The efficacy of continued feeding of specific IgY before and after exposure to the pathogenic bacteria has yet to be explored.

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