The lipid moiety of a novel recombinant lipoprotein, which contains a dengue virus envelope protein domain 3, rlipo-D1E3, has been shown to activate antigen-presenting cells (APCs) as an intrinsic adjuvant. Because the lipid moiety of rlipo-D1E3 contains an unsaturated fatty acid, it is unclear if the receptor usage by bacterially derived lipoproteins is the same as that of the synthetic lipopeptide palmitoyl-3-Cys-Ser-(Lys)4 (Pam3). In the present study, we show that the rlipo-D1E3 lipoprotein can induce the activation of spleen cells and bone marrow-derived dendritic cells (BM-DCs) in wild-type and TLR4-deficient mice, but not in TLR2-/- mice. After analyzing the co-receptor usage of TLR2 using TLR1-/- or TLR6-/- mice, the TLR2 signaling triggered by rlipo-D1E3 and Pam3 could use either TLR1 or TLR6 as a co-receptor. Analysis of the MAPK signaling pathway revealed that rlipo-D1E3 could initiate the phosphorylation of p38, ERK1/2 and JNK1/2 earlier than the synthetic lipopeptide. In addition, the expression levels of IL-23, IL-27 and MIP-1α in BM-DCs stimulated by rlipo-D1E3 were higher than the expression levels in BM-DCs stimulated by Pam3. Taken together, these results demonstrate that different TLR2 ligands can promote various immune responses by inducing different levels of biological cytokines and chemokines.
