Immunization of rainbow trout Oncorhynchus mykiss against Discocotyle sagittata (Monogenea)

[摘要] ABSTRACT: Rainbow trout Oncorhynchus mykiss were injected intraperitoneally with 2 different Discocotyle sagittata extracts dissolved in PBS and subsequently exposed to controlled infection. Immunization resulted in significantlyreduced (p < 0.0001) worm intensities in >50% of vaccinated fish (response arbitrarily defined as parasite burdens < mean control intensity - 1 SD), irrespective of the immunization regime (different parasite extracts, dosing and applicationschedules) employed. The protective effect of worm extract applied in Freund¹s complete adjuvant (FCA) did not differ significantly from extract given in PBS. Vaccination with embryonated parasite eggs extract and with FCA alone did not result in partialimmunity, suggesting the observed protective effect is specific. Immunized fish had significantly higher specific antibody titres at the time of dissection (as determined by ELISA) than both naïve and control fish. Overall, a significant negativecorrelation was found between antibody titres and worm burdens, suggesting immunoglobulins are implicated in mediating partial immunity. Western blot tests indicated the 2 different worm extracts used to immunize fish share antigens, but each oneprimarily induced recognition of a distinct band (30 and 38 kDa). Immunization seems to promote a shift between 2 equilibria, rather than progressively increasing protection. This would explain why boosting did not increase immunity, and why 2 differentextracts primarily inducing recognition of 2 distinct antigens provide similar degrees of protection. Although several other non-specific and cellular factors are likely to be involved in controlling parasite numbers, it cannot be excluded that antibodiescould be involved in mediating the observed partial immunity.

[学科分类] 生物科学（综合）

[关键词] Oncorhynchus mykiss;Trout;Monogenea;Discocotyle sagittata;Immunization;Antibodies