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

In order to evaluate the adjuvant activity in fish of polar glycopeptidolipids fromMycobacterium chelonae(pGPL-Mc), salmonids were injected with pGPL-Mcalone or in combination withAeromonas salmonicidabacterin. Side-effects, antibody production againstA. salmonicidaand lymphocyte stimulation were studied. Twelve weeks after vaccination, the antibody responses of fish injected with 0·25 mg kg−1pGPL-Mcin 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-Mcreduced the levels of specific antibodies. The lymphocyte responses to lipopolysaccharide (LPS), a potent B-cell mitogen, were higher in rainbow trout injected with pGPL-Mcalone, compared to the fish injected with saline, suggesting B-cell activation as a mechanism. pGPL-Mcshowed 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-Mcan interesting candidate adjuvant for incorporation in future vaccine formulations.