Comprehensive and integrative analyses of genetics, transcription, and pathway modeling on LS and non-LS indicates that these sarcoidosis phenotypes have different genetic susceptibility, genomic distributions, and cellular activities, suggesting distinct molecular mechanisms in pathways related to immune response with a common region.

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Löfgren's syndrome (LS), first described in 1946 by Swedish Professor of Medicine Sven Löfgren, is a clinically distinct phenotype of sarcoidosis. Patients typically experience an acute disease onset, usually with fever, and characteristic symptoms of bilateral hilar lymphadenopathy, erythema nodosum, and/or bilateral ankle arthritis or periarticular inflammation. LS patients are well documented to have a good prognosis, which is especially true for HLA-DRB1*03+ individuals. The presence of this allele correlates closely with an accumulation of clonal CD4+ T-cell populations in the lung, suggestive of local antigen recognition. Moreover, LS differs markedly from “non-LS” sarcoidosis regarding immune cell activation, differentiation, and regulation, which may influence clinical outcome and spontaneous disease resolution.This review offers an overview of the clinical characteristics, genetic background, and immunological characteristics of LS, as well as patient management, and reflections on future scientific challenges, emphasizing the concept of LS as a disease in its own right.