[Resiquimod (R848) has more stronger immune adjuvantivity than other tested TLR agonists]

Objective To compare and characterize the Th1 immune responses induced by the most commonly used commercial Toll-like receptor (TLR) agonists through in vivo and ex vivo experiments. Methods The concentrations of IL-12 were tested by ELISA after mouse dendritic cells (DCs) in vitro were stimulated by one of tested TLR agonists, including poly(I:C), monophosphoryl lipid A (MPLA), resiquimod (R848), cytosine polyguanine-C (CpG-C). The changes in percentage and phenotype of DCs, NK cells and effector T cells in the draining lymph nodes were analyzed by flow cytometry after BALB/c mice were immunized with ovalbumin (OVA) mixed with selected TLR agonist. The serum concentrations of specific anti-OVA IgG2a in the immunized mice were determined by ELISA. Results Only CpG-C and R848 could significantly induce the production of IL-12 from bone marrow-derived DCs in vitro. Among the tested TLR agonists, R848 was the most effective adjuvant in recruiting DCs and NK cells into lymph nodes, inducing the proliferation of CD4⁺ and CD8⁺ effector T cells and the production of specific anti-OVA IgG2a in vivo. Conclusion R848 was the most potential Th1-promoting adjuvant among the tested TLR agonists.