Adjuvanticity of an Ornithine-Containing Lipid of Flavobacterium meningosepticum as a Candidate Vaccine Adjuvant

Ornithine-containing lipids (OrnL) extracted from Flavobacterium meningosepticum have been reported to have various biological activities such as B-cell mitogenicity and macrophage activation to generate interleukin-1 and prostaglandin E2. We, using ovalbumin (OVA) as an antigen, evaluated the adjuvant activity of OrnL as an immunological adjuvant in BALB/c mice. OrnL showed the function of forming liposome-like vesicles retaining biological activities when prepared as either small unilamellar or dehydration-rehydration vesicles. Although OrnL was not shown to have enough entrapping efficacy for use as a vaccine adjuvant, phosphatidylglycerol (PG) and cholesterol (CHOL) added to stabilize the vesicle membrane increased the entrapping efficacy to the same extent as that of conventional liposomes. Furthermore, the stabilized OrnL vesicles tolerated centrifugation to remove non-entrapped antigens. Completely antigen-entrapped OrnL vesicles including PG and CHOL induced a significantly greater enhancement of IgG antibody production than did aluminum hydroxide gel in BALB/c mice from week 6. These results indicate that OrnL can be utilized as an immunological adjuvant for vaccines.