TY - JOUR

T1 - Primary immunization using low antigen dosages and immunological tolerance in rainbow trout

AU - Marana, M. H.

AU - Chettri, J. K.

AU - Salten, M. Brahe

AU - Bach-Olesen, N. Emmervadt

AU - Kania, P. W.

AU - Dalsgaard, I.

AU - Buchmann, K.

PY - 2020

Y1 - 2020

N2 - Enteric redmouth disease (ERM), caused by the Gram negative enterobacterium Yersinia ruckeri, affects farming of salmonids, but vaccination against ERM confers a certain degree of protection dependent on the administration route. Recent studies on oral vaccination of rainbow trout suggest that immunological tolerance may be induced by primary immunization using a low antigen dosage. We have examined if low dosages of Y. ruckeri antigens, applied in feed or bath exposure over a prolonged period of time, leave rainbow trout more susceptible to infection. Groups of rainbow trout were immunized, either by immersion or feeding using different vaccine dosages, and subsequently challenged by live Y. ruckeri. Survival was recorded and immune reactions in surviving fish were evaluated (ELISA and qPCR). Trout, bath-vaccinated in a highly diluted vaccine or fed the same amount of bacterin in feed over 10 days, were not protected against Y. ruckeri challenge infection and in some cases these sub-optimally immunized fish experienced lower survival compared to non-primed controls. Genes encoding FoxP3 and immune-suppressive cytokines were down-regulated in fish vaccinated with a high antigen dosage when compared to groups exposed to low antigen dosages, suggesting a higher regulatory T cell activity in the latter fish groups. The study suggests that repeated exposure to low antigen concentrations induces some degree of immune tolerance in rainbow trout and we recommend application of high antigen dosages for primary immunization of trout.

AB - Enteric redmouth disease (ERM), caused by the Gram negative enterobacterium Yersinia ruckeri, affects farming of salmonids, but vaccination against ERM confers a certain degree of protection dependent on the administration route. Recent studies on oral vaccination of rainbow trout suggest that immunological tolerance may be induced by primary immunization using a low antigen dosage. We have examined if low dosages of Y. ruckeri antigens, applied in feed or bath exposure over a prolonged period of time, leave rainbow trout more susceptible to infection. Groups of rainbow trout were immunized, either by immersion or feeding using different vaccine dosages, and subsequently challenged by live Y. ruckeri. Survival was recorded and immune reactions in surviving fish were evaluated (ELISA and qPCR). Trout, bath-vaccinated in a highly diluted vaccine or fed the same amount of bacterin in feed over 10 days, were not protected against Y. ruckeri challenge infection and in some cases these sub-optimally immunized fish experienced lower survival compared to non-primed controls. Genes encoding FoxP3 and immune-suppressive cytokines were down-regulated in fish vaccinated with a high antigen dosage when compared to groups exposed to low antigen dosages, suggesting a higher regulatory T cell activity in the latter fish groups. The study suggests that repeated exposure to low antigen concentrations induces some degree of immune tolerance in rainbow trout and we recommend application of high antigen dosages for primary immunization of trout.

KW - Aquaculture

KW - Immunological tolerance

KW - Rainbow trout

KW - Vaccination

KW - Yersinia ruckeri

U2 - 10.1016/j.fsi.2020.06.049

DO - 10.1016/j.fsi.2020.06.049

M3 - Journal article

C2 - 32619627

AN - SCOPUS:85087352654

VL - 105

SP - 16

EP - 23

JO - Fish and Shellfish Immunology

JF - Fish and Shellfish Immunology

SN - 1050-4648

ER -