Effect of different adjuvants on the humoral immune response of rainbow trout

Abstract

The mechanism of the adjuvant effect on an immune system has been investigated in mammals but is not yet completely understood. It would seem that the retention of the antigen at the site of injection and its slow distribution in the organism plays a major role in prolonging stimulation. Meanwhile, undesirable secondary effects due to Freund's complete adjuvant (FCA) are well known in mammals (eg : production of local granuloma, autoimmune diseases, sensitization to tuberculin (i). This is why research has been undertaken to localize the peptidoglycan sequence in the cell wall of mycobacteria capable of adjuvanticity with no secondary effects ; muramyldipeptide (MDP) is that minimal structure and is now industrially synthetized (i) Before this study, MDP had never been tested in fish, whereas experimental immunology in fish has widely used FCA intraperitoneally in Rainbow Trout to enhance the humoral response to dinitrophenol-haemocyanin (DNP-KLH) (2), killed Aeromonas salmonicida (3), (4), or soluble bovine serum albumin (5) . POST (6) who injected FCA with killed Aeromonas hydrophila in muscles, observed a strong inflammatory reaction with a sterile abscess, sometimes open with secondary infections, as observed in mammals with FCA. FCA and Freund's incomplete adjuvant (FIA) are the most commonly used in fish, but twice, authors have reported the use of Klearol and Arlacel (9 :i v/v) with killed bacteria on Sockeye Salmon (7) or Rainbow Trout (3). In our study, we tested four adjuvants which had never been previously tested in fish : aluminium hydroxide and saponin, water in oil (B) and oil in water (A) emulsions and MDP, and compared their performances to FCA and FIA which are already known. Aluminium hydroxide AI(OH) 3 mixed with saponin is the adjuvant used in Foot and Mouth disease vaccine. Saponin has a high enhancing effect on immune response, but can sometimes be toxic, so this potential toxicity is decreased by aluminium hydroxide gel (8). Successful trials have been reported in fish with A1 (OH) (9), but 3 results were inferior to those obtained with FCA. Different oily emulsions are often used for viral vaccines :for example Newcastle Disease (poultry) and various mammal-specific vaccines (i0)