Immunopotentiators activate innate immunity directly (for example, cytokines) or through pattern-recognition receptors (PRRs, such as those for bacterial components). The Toll-like receptors (TLRs) are a family of PRRs that are an important link between innate and adaptive immunity. Some studies have shown that TLR ligands have adjuvant activity and enhance antigen-specific antibody and cell-mediated immune responses, especially when they are combined with delivery systems that promote their uptake and delivery into antigen-presenting cells [22–24]. For clinical studies, TLR9 is generally stimulated with synthetic oligodeoxynucleotides containing one or more unmethylated CpG dinucleotides. In humans, CpG has been used as an adjuvant for infectious disease vaccination [25,26] and in the development of cancer therapy [27]. In a mouse model, CpG has also been shown to induce T helper 1 (Th1) immune responses, which are characterized by the production of IFN-γ and the generation of IgG2a [28,29]. Moreover, a previous study had demonstrated that different liposomes with CpG ODN significantly increased Th1-biased cytokines and augmented cell mediated immune response [30].
