Characterization of oral microbiome in atopic dermatitis patients treated with dupilumab or upadacitinib

Abstract Objectives Dysbiosis, an imbalanced state of microbial communities in the human body, may contribute to autoimmune diseases such as atopic dermatitis (AD). While the role of affected skin-gut microbiome axis in AD is well established, still little is known about the relationship between oral microflora-based dysbiosis and AD progression and treatment. Materials and methods 16S rRNA gene amplicon sequencing of the V3–V4 hypervariable region was used to characterize the bacterial profiles of saliva samples from fifteen AD patients treated with dupilumab, an antibody against interleukin-4 receptor, or upadacitinib, an inhibitor of JAK1 kinase, for sixteen weeks. Oral microbiome data were compared with the Eczema Area and Severity Index (EASI). Results Analysis revealed that at phylum level, Actinomycetota decreased significantly upon treatment (from a median of 11.87% to 6.15%; q = 0.0094), with a reciprocal increase in Bacteroidota (from 19.78% to 28.39%; q = 0.0185). Conclusions Although all patients showed clinical improvement, the cohort did not permit assessment of a dose–response relationship between EASI score and Actinomycetota abundance. Thus, larger, more heterogeneous cohorts and mechanistic data (e.g., metabolomics-based identification of microbiome-derived metabolites) are needed to validate these findings and clarify their relevance as a potential therapeutic marker in AD. Clinical relevance The parallel decline in oral Actinomycetota abundance and EASI score highlights a potential link between the oral microbiome and treatment response in AD, warranting further investigation. In the absence of non-responders, this association does not yet support Actinomycetota as a potential biomarker of treatment efficacy.