Detection of the BRAF mutation in multiple myeloid cell types isolated from LCH lesions of SS LCH patients. (A) FFPE biopsy taken from the osteolytic lesion in the skull of UFB patient LCH_025. IHC was performed to stain LC-like cells (CD207, CD1a), MGCs, and MΦs (CD68 and morphology). Cells expressing mutant BRAF^V600E protein were detected with VE-1 antibody. (B) Detection of the BRAF^V600E mutation in MGCs and CD68⁺ LCs/MΦs microdissected from the skull lesion of patient LCH_025 by ddPCR; (C) IHC depicting CD1a⁺ LCH cells in the lesion of MFB patient LCH_009. (D) ddPCR 2-dimensional plot depicting BRAF^V600D mutation detection in microdissected lesional CD1a⁺ cells of MFB patient LCH_009. (E) Gating strategy for flow cytometric sorting of HLA-DR⁺CD14⁺CD11c⁺CD1a⁺ LC-like cells and HLA-DR⁺CD14⁺CD11c⁺CD1a⁻ Mo’s/MΦs from cryopreserved lesional cells of patient LCH_009. (F) Two-dimensional ddPCR plot depicting BRAF^V600D mutation detection in sorted LC-like cells and Mo’s/MΦs of patient LCH_009.