Adjuvant Activity of Synthetic Lipid A of , a Gut-Associated Lymphoid Tissue-Resident Commensal Bacterium, to Augment Antigen-Specific IgG and Th17 Responses in Systemic Vaccine.

spp. are identified as commensal bacteria and have been found to inhabit Peyer's patches in the gut. We previously reported that -derived lipopolysaccharides (LPS) exerted adjuvant activity in systemic vaccination, without excessive inflammation. Lipid A is one of the components responsible for the biological effect of LPS and has previously been applied as an adjuvant. Here, we examined the adjuvant activity and safety of chemically synthesized lipid A. We found that levels of OVA-specific serum IgG antibodies increased in mice that were subcutaneously immunized with ovalbumin (OVA) plus lipid A relative to those that were immunized with OVA alone. In addition, lipid A promoted antigen-specific T helper 17 (Th17) responses in the spleen; upregulated the expression of MHC class II, CD40, CD80, and CD86 on bone marrow-derived dendritic cells (BMDCs); enhanced the production of Th17-inducing cytokines IL-6 and IL-23 from BMDCs. Stimulation with lipid A also induced the production of IL-6 and IL-1β in human peripheral blood mononuclear cells. Moreover, lipid A caused minor side effects, such as lymphopenia and thrombocytopenia. These findings suggest that lipid A is a safe and effective Th17-type adjuvant by directly stimulating dendritic cells in systemic vaccination.