T-cell immunoglobulin and mucin domain-containing protein 3–mediated immunomodulation in myeloid cells and keratinocytes in the development of severe acne

Acne vulgaris is a common chronic inflammatory skin disorder with significant clinical and societal impacts. Severe acne (SA), in particular, causes scarring, disfigurement, and psychosocial distress. The underlying pathogenesis of SA remains poorly understood, hindering the development of effective treatments. In our study, single-cell RNA sequencing (scRNA-seq) of samples from SA, acne, and normal skin was performed, 12 clusters were identified from the total cell population, and macrophages were considered as important cell clusters since all gene modules showed high gene activity for macrophages in the scRNA weighted correlation network analysis (WGCNA). By integrating macrophage-specific differentially expressed genes (DEGs) with Mendelian randomization (MR) analysis, it was found that T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3) was identified as a potential immune checkpoint involved in the development of SA. Multiplex immunohistochemistry (mIHC) revealed a decreased tendency for TIM3⁺ neutrophils, an increased presence of TIM3⁺ macrophages (especially TIM3⁺ M2 macrophages), and a reduced population of TIM3⁺ keratinocytes in SA tissues compared to controls. In human immortalized keratinocytes (HaCaT) cells, TIM3 knockdown led to the upregulation of Propionibacterium acnes (P. acnes)-induced proinflammatory cytokine secretion, and the administration of an anti-Tim3 antibody in P.acnes induced mouse model exacerbated acne-associated inflammation. Collectively, these findings support a role for TIM3 in SA and suggest TIM3 as a potential therapeutic target, while underscoring the immunomodulatory function of keratinocytes and providing directions for future investigations.