LCH : Birbeck Granules
With transmission electron microscopy (TEM), Langerhans cells show characteristic Birbeck granules which differentiate them from other mononuclear phagocytes. They are zipper-like pentalaminar tubules, frequently with a dilated end that creates a tennis racket-like appearance. They measure 200-400 nm in length and 33 nm in width. The dilated portion contains the protein langerin (CD207).
TEM was the gold standard for many years for the diagnosis of Langerhans cell histiocytosis. With the availability of specific immunohistochemical markers like CD1a and CD207, TEM is rarely used these days.
Image courtesy of: John Brealey (@JohnBrealey), Senior Medical Scientist, Electron Microscopy Unit, SA Pathology, Australia; used with permission.