Immunofluorescence analysis of BRAF pathway activation in LCH. (A) LCH sample stained with DAPI (blue), anti-CD1a (green), antiphospho-MEK (red), and a merged image of all 3 stains. (B) LCH sample stained with DAPI (blue), anti-CD1a (green), antiphospho-ERK (red), and a merged image of all 3 stains. Arrowheads indicate CD1a-negative cells that are also negative for phospho-MEK and phospho-ERK. (Technical details described in supplemental Methods.)