Background: Idiopathic inflammatory myopathies (IIM) comprise a heterogeneous spectrum of systemic autoimmune diseases with overlapping clinical features but divergent immunopathological mechanisms. Anti–melanoma differentiation–associated gene 5 antibody–positive dermatomyositis (MDA5-DM) is a biologically distinct IIM subset characterised by rapidly progressive interstitial lung disease, hyperferritinaemia, and high mortality. In contrast to other IIM subtypes, accumulating evidence indicates that MDA5-DM is driven predominantly by innate immune activation and excessive interferon (IFN) signalling rather than classical adaptive immune cytotoxicity. Recent integrative multi-omics studies have highlighted central roles for type I, II, and III IFN pathways, macrophage activation, and autoantibody-associated immune amplification in shaping MDA5-DM pathobiology. We previously reported that a multitargeted therapeutic strategy combining baricitinib, rituximab, and tacrolimus (BRT therapy) improved survival in severe MDA5-DM, accompanied by suppression of IFN signatures and B-cell–related gene expression [1]. However, the pre-treatment immune architecture distinguishing MDA5-DM from other IIM subsets, and its implications for rational therapeutic targeting, remain incompletely defined.

Objectives: To define the immune architecture distinguishing MDA5-positive dermatomyositis from other idiopathic inflammatory myopathies using peripheral blood transcriptomics and to determine whether disease-specific immune networks inform rational therapeutic targeting.

Methods: Pre-treatment peripheral whole-blood transcriptomic profiling was performed in 46 patients with idiopathic inflammatory myopathies, including 12 anti-MDA5–positive and 34 anti-MDA5–negative cases (including anti–aminoacyl-tRNA synthetase antibody–positive patients). Differentially expressed genes (DEGs) were identified using |fold change| ≥1.5 and p <0.05, yielding 1,570 DEGs. Weighted gene co-expression network analysis (WGCNA) was applied to identify disease-associated gene modules. Module eigengenes were correlated with anti-MDA5 antibody status and interferon signature scores, followed by pathway enrichment and hub gene analyses to delineate immune processes underlying MDA5-DM within the IIM spectrum.

Results: WGCNA identified 11 gene co-expression modules separating MDA5-positive from MDA5-negative IIM. A Blue module showed strong positive associations with anti-MDA5 antibody status and interferon signature scores and was enriched for type I and III IFN signalling, interferon-stimulated genes, and Toll-like receptor–mediated innate immune sensing, with STAT1, STAT2, IRF5, and IRF7 as central hub regulators, defining a dominant interferon-driven innate immune initiation programme. A distinct Black module was enriched for complement activation, pathogen phagocytosis, and oxidative damage, delineating a macrophage-centred inflammatory amplification axis downstream of interferon activation. In addition, a Pink module showed enrichment of interleukin-1–related inflammatory signalling and B-cell receptor–associated pathways, identifying immune networks involved in cytokine-driven inflammatory propagation and autoantibody-associated immune amplification that likely sustain systemic inflammation in MDA5-DM. By contrast, modules associated with cytotoxic T-cell responses, sphingosine-1-phosphate and GPCR signalling, and TGF-β–related pathways, including lung fibrosis–associated signatures, were relatively downregulated in MDA5-positive patients, indicating temporal quiescence of adaptive cytotoxicity and fibrotic remodelling during the acute, pre-treatment phase

Conclusions: By analysing idiopathic inflammatory myopathies as a unified disease spectrum and contrasting MDA5-positive with MDA5-negative cases, this transcriptomic network study demonstrates that MDA5-DM is immunologically distinct within IIM. These modules can be conceptualised as a Blue–Black–Pink hierarchy, in which interferon-driven innate immune initiation is followed by macrophage-centred inflammatory amplification and sustained cytokine- and autoantibody-associated immune propagation. Importantly, this disease-specific immune architecture provides a mechanistic explanation for the efficacy of multitargeted therapeutic strategies. Within the upstream interferon-driven axis, JAK1/2 inhibition with baricitinib suppresses type I, II, and III interferon signalling, attenuating the interferon-dominant Blue module and indirectly dampening downstream macrophage activation. Among currently available JAK inhibitors, baricitinib provides comparatively greater functional inhibition of JAK2-dependent pathways, which may confer enhanced suppression of IFN-γ– and GM-CSF–associated macrophage activation relative to agents with predominant JAK1/3 selectivity, including tofacitinib. B-cell depletion with rituximab targets autoantibody-associated immune amplification and B-cell receptor–dependent inflammatory propagation within the Pink module, while calcineurin inhibition with tacrolimus further constrains cytokine-mediated immune activation across downstream inflammatory pathways. Viewed through this integrated framework, the favourable outcomes observed in our pilot study of BRT therapy are biologically coherent. Collectively, these findings provide a mechanistic rationale for multitargeted, disease-adapted therapeutic strategies in severe MDA5-DM and underscore the utility of peripheral blood transcriptomics in bridging disease mechanisms with rational therapeutic design.

REFERENCES: [1] Tokunaga, M. et al. A pilot transcriptomic study of a novel multitargeted BRT regimen for anti-MDA5 antibody-positive dermatomyositis: improving survival over conventional therapy. Frontiers in immunology 16, 1568338 (2025).

Acknowledgments: NIL.

Disclosure of Interests: Yoshinobu Koyama Taisho Pharma, Biogen Inc., Novartis AG, Ono Pharma, Yoshiharu Sato: None declared, Yu Nakai: None declared, Yoshinori Nishiura: None declared, Kenta Shidahara: None declared.