RNA in situ hybridization for ISG15 and IFI6 highlights IFN-I activity in discoid lupus erythematosus

IFN-I signaling is a hallmark of discoid lupus erythematosus (DLE), but routine tissue-based assays to detect this pathway are limited. Re-analysis of public transcriptomic data identified ISG15 and IFI6 as candidate IFN markers, ranking among the top differentially expressed genes in DLE datasets. We performed RNA in situ hybridization for both markers on archival specimens from DLE (n =11), other inflammatory dermatoses (n = 11; atopic dermatitis, psoriasis, lichen planus), and controls (n = 8). A total of 81 slides were scored (0-4+) in epidermal and dermal compartments. RNA in situ hybridization showed strong staining in basal keratinocytes and dermis of DLE, with deep dermal positivity in 89% of specimens with sufficient depth for analysis. Deep staining was absent in controls and other dermatoses. DLE demonstrated significantly higher staining intensity than inflammatory controls (P < .001). RNA in situ hybridization for ISG15 and IFI6 identifies IFN activation in DLE, distinguishing it from other dermatoses and providing objective molecular evidence applicable to routine specimens.