Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by the presence of pathogenic autoantibodies and a substantial influx of immune cells into skin lesions. However, the role of eosinophils in BP remains inadequately elucidated.

We sought to determine the pathologic involvement of eosinophils and eosinophil extracellular traps (EETs) in BP.

Human samples collected from BP patients and healthy controls were utilized to explore the potential role of eosinophils and their EETs in BP patients through serologic detection, flow cytometry, and immunofluorescence. Naive CD4⁺ T cells isolated from healthy donors were stimulated and subjected to further analysis via RNA sequencing. We additionally evaluated the potential of targeting EETs in BP180-immunized BP-like mice and in in vitro settings.

We found that elevated levels of eosinophils and EETs in BP patients correlated with disease severity. The DNA components within EETs played a crucial role in driving the differentiation of naive CD4⁺ T cells into follicular helper T (Tfh) cells by activating coil domains containing 25 (CCDC25). Treatment with DNase I, which disrupts the structural integrity of EETs, or neutralizing antibody against CCDC25 reduced the expansion of Tfh cells and suppressed the production of autoantibodies in BP180-immunized BP-like mouse models. Additionally, we discovered that EETs induced the N⁶-methyladenosine methylation of the transcription factor musculoaponeurotic fibrosarcoma (MAF) via the DNA-CCDC25-VIRMA pathway, thereby enhancing its mRNA stability and promoting Tfh cell differentiation.

Our study revealed a previously unrecognized mechanism by which EETs trigger abnormal Tfh cell differentiation through CCDC25, followed by Vir-like m⁶A methyltransferase–associated protein (VIRMA)-mediated N⁶-methyladenosine modification of MAF. These insights provide promising avenues for the development of targeted therapeutic interventions in the field of BP and potentially other autoimmune diseases.