Imiquimod promotes Th1 and Th17 responses via NF-κB-driven IL-12 and IL-6 production in an in vitro co-culture model.

Although imiquimod (IMQ) is widely used to induce psoriasis-like inflammation in mouse models, its direct effects on dendritic cells (DCs) and their capacity to drive T cell polarization remain poorly defined. The systemic complexity of in vivo models hinders the ability to delineate the direct, cell-intrinsic effects of IMQ. To address this gap, an in vitro DC-CD4(+) T cell co-culture system was established using bone marrow-derived DCs and naïve CD4(+) T cells isolated from OT-II mice, enabling precise evaluation of the direct immunomodulatory effects of IMQ. IMQ treatment markedly upregulated maturation markers (CD40, CD80, CD86 and major histocompatibility complex class II), and increased IL-12 and IL-6 secretion in a dose-dependent manner. These effects were significantly attenuated by NF-κB inhibitors (caffeic acid phenethyl ester and Bay 11-7082), indicating a critical role for NF-κB signaling in DC activation. When co-cultured with naïve CD4(+) T cells, IMQ-treated DCs promoted robust differentiation toward T helper (Th)1 and Th17 subsets. Neutralization of IL-12 and IL-6 in the co-culture system significantly reduced the frequencies of Th1 and Th17 cells and their cytokine output, confirming that these responses were mediated by DC-derived cytokines. Collectively, the present findings demonstrated that IMQ directly activated DCs via NF-κB signaling and induced pathogenic Th cell responses through IL-12 and IL-6 production. By eliminating confounding in vivo factors, the present study provided evidence for the DC-intrinsic effects of IMQ and offered mechanistic insights into the cellular pathways linking innate immune sensing to adaptive T cell responses in psoriasis.