Immunostimulatory activity and safety evaluation of Bordetella bronchiseptica-derived lipopolysaccharide, a new vaccine adjuvant candidate.

Adjuvants are used to elicit strong immune responses for vaccines that show poor immunogenicity. Previously, we demonstrated that a sonicated bacterin of Bordetella bronchiseptica can be used as a safe adjuvant that enhances the antigen-presenting capability of dendritic cells (DCs). In this study, we purified the lipopolysaccharide (LPS) of B. bronchiseptica (Bb-LPS) and investigated its immunogenic effects on DCs compared to those of Escherichia coli O26:B6 (O26)-derived LPS (O26-LPS), a positive control. Bb-LPS was purified using an LPS extraction kit. Limulus amebocyte lysate assay was performed to determine the optimal concentration of Bb-LPS and O26-LPS for treatment. Bb-LPS increased the metabolic activity of DCs at a concentration of 0 to 250 EU/mL, similar to that of O26-LPS. Bb-LPS significantly increased the expression level of CD40 and CD54, related to the immune responses of DCs. Bb-LPS enhanced the antigen-presenting capability of DCs and significantly increased the interferon-gamma/interleukin-4 ratio of CD4 T cells co-cultured with DCs to 0.95 (p < 0.05). Moreover, Bb-LPS increased the production of pro-inflammatory cytokines in a safer manner than that obtained by O26-LPS. In vivo safety tests revealed that Bb-LPS was less toxic than O26-LPS in mice. This study demonstrated that Bb-LPS showed unique immune characteristics and immunogenic effects on the antigen-presenting capability of DCs, which differed from those of O26-LPS. This study provides valuable information for basic and clinical research for developing safe vaccine adjuvants.