Repeated imiquimod challenge as an experimental model of psoriasiform inflammation and re-exposure associated reactivation

Long-term psoriasis management remains a major challenge worldwide. Although repeated imiquimod (IMQ) application has been used to mimic psoriatic inflammatory reactivation, it remains unclear whether this approach reflects amplified acute inflammation or the emergence of tissue-resident, memory-associated features. Here, we established a repeated IMQ-challenge model (IMQ-R) and compared it with a single-course IMQ model (IMQ-S) and human psoriatic lesions using bulk RNA sequencing (bulk RNA-seq) and single-cell RNA sequencing (single-cell RNA-seq). During the final induction phase, IMQ-R showed a more rapid re-emergence of skin inflammation than IMQ-S and displayed features of inflammatory reactivation in previously challenged skin, including IL-17-related pathways, TRM-related T-cell features, and predicted multicellular communication patterns. Single-cell analysis showed that IMQ-R exhibited a cellular composition more similar to active human psoriatic skin than IMQ-S, with keratinocyte (KC) expansion, endothelial cell (EC) enrichment, and relative preservation of T-cell populations. T-cell subsets with memory-associated annotations, including central memory T cells (TCM) and tissue-resident memory T cells (TRM), were increased in IMQ-R. In particular, IMQ-R was associated with enrichment of TRM17-related transcriptional features and enhanced predicted communication among T cells, keratinocytes (KCs), and myeloid cells, including IL-17-related signaling pathways. In summary, repeated IMQ challenge generates a psoriasiform model with accelerated inflammatory re-emergence and TRM-related features during re-exposure that are not fully captured by the conventional acute IMQ model. This model provides a useful platform for studying inflammatory reactivation after repeated challenge and for evaluating interventions targeting cutaneous memory-associated inflammatory programs.