Spatial transcriptomics reveals mechanism of autoimmunity driven by internalised autoantibodies.

OBJECTIVES

Autoantibody internalisation has been implicated in autoimmune disease pathogenesis, yet its mechanisms and generalisability across diseases, cell types, and tissues remain poorly defined. We sought to address these gaps.

METHODS

Bulk RNA sequencing was performed on 814 muscle biopsies from patients with autoimmune diseases and healthy controls, including an external validation cohort of 41 additional samples. Purified patient immunoglobulin (Ig) G was electroporated into primary human cells to assess functional effects in vitro. Immunofluorescence evaluated localisation of immunoglobulins across diseases and tissues. Spatial transcriptomics assessed disease-specific gene expression, cellular injury, and inflammatory responses.

RESULTS

Using anti-Mi2 dermatomyositis and anti-PM/Scl scleromyositis as model diseases, we validated reproducible, autoantibody-specific transcriptomic signatures consistent with autoantigen dysfunction across cohorts and confirmed that electroporation of purified patient IgG into healthy primary cells recapitulates these disease-associated transcriptional programmes. Spatial transcriptomics linked these signatures to cellular injury and distinct inflammatory responses, including activation of type I interferon and TGFβ signalling in anti-Mi2 dermatomyositis and type II interferon signalling in anti-PM/Scl scleromyositis. These programmes were observed predominantly not only in muscle fibres but also in macrophages, endothelial cells, and fibroblasts/fibroadipogenic progenitors. Spatial transcriptomics further revealed transfer of immunoglobulin RNA from antibody-secreting cells to adjacent target cells expressing disease-specific transcriptional programmes. Antibody internalisation, previously described in myositis muscle, was also observed in skin from patients with anti-Mi2 and anti-PM/Scl and in tissues from anti-U1RNP mixed connective tissue disease, anti-Ku overlap syndrome, and anti-Scl70 systemic sclerosis.

CONCLUSIONS

Together, these findings establish autoantibody internalisation as a mechanism of tissue injury in autoimmunity, suggesting its broader relevance across autoantibody-mediated diseases.