Formation of Birbeck granules in cultures of CD1c⁺ DCs. (A) EM images of Birbeck granules in CD1c⁺ DCs cultured for 7 days showing classical “tennis racket” morphology, pentalaminar structure, and formation by endocytosis. Insets in the top left panel are displayed beneath and to the right. The experiment was performed twice with 2 different donors only with GM-CSF and BMP7. The entire culture was processed for EM. (B) Comparison of the number of Birbeck granules per cell section between CD14⁺ monocytes and CD1c⁺ DC cultures. *P < .01. (C) Extended phenotype of LC-like cells (CD1c⁺) compared with primary Langerhans cells (Langerhans). Shaded histograms, isotype controls; gray line, CD1a and langerin double-negative cells; black line, CD1a⁺ langerin⁺ cells. Similar results were obtained with GM-CSF and TGFβ, BMP7, or a combination of both in 3 different donors; 1 of 3 experiments performed with GM-CSF, TGFβ, and BMP7 is shown. (D) Comparison of langerin, EpCAM, and CD11b expression in CD1c⁺ DCs and CD14⁺ monocytes. Light gray, isotype; midgray, CD1a⁺ langerin^low cells; black, CD1a⁺ langerin^high cells. One of three experiments performed with GM-CSF, TGFβ, and BMP7 is shown.