Adjuvant activity of polar glycopeptidolipids fromMycobacterium chelonaein experimental vaccines againstAeromonas salmonicidain salmonid fish

Abstract In order to evaluate the adjuvant activity in fish of polar glycopeptidolipids from Mycobacterium chelonae (pGPL- Mc ), salmonids were injected with pGPL- Mc alone or in combination with Aeromonas salmonicida bacterin. Side-effects, antibody production against A. salmonicida and lymphocyte stimulation were studied. Twelve weeks after vaccination, the antibody responses of fish injected with 0·25 mg kg −1 pGPL- Mc in addition to bacterial antigen were significantly stronger than those in fish injected with a non-adjuvanted bacterin, and insignificantly lower than the antibody titres achieved with an oil-adjuvanted reference vaccine. Higher doses of pGPL- Mc reduced the levels of specific antibodies. The lymphocyte responses to lipopolysaccharide (LPS), a potent B-cell mitogen, were higher in rainbow trout injected with pGPL- Mc alone, compared to the fish injected with saline, suggesting B-cell activation as a mechanism. pGPL- Mc showed a weak dose-dependent mitogen effect on fish leucocytes. No significant side-effects were observed after intraperitoneal injection of pGPL- Mc . The relatively long-term immunostimulation in fish with no side-effects makes pGPL- Mc an interesting candidate adjuvant for incorporation in future vaccine formulations.