Occurrence of “Cored Tubule” in the Birbeck Granule-containing Cells of Mice

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Abstract
A unique tubular structure having a central core has been observed in the Birbeck granule-containing cells in the epidermis, dermis and lymph nodes of mice. Based on its morphology this structure was tentatively named “cored tubule.” In the electron micrographs, it appeared quite similar to the Birbeck granules present in the same cells, but is tubular in shape and entirely different from the disc-shaped Birbeck granules. The cored tubules were about 30 nm in diameter, while Birbeck granules were about 43 nm in thickness. By branching or anastomosing, cored tubules usually formed a network, which often surrounded a spheroid body, making a unique structural complex. In the epidermis, dermis and lymph nodes, the ultrastructural features of the cells containing cored tubules and/or Birbeck granules are quite similar. These cells were considered to belong to the same cell type, and it may be one of the macrophages. The function of the cored tubules in these cells remains to be investigated.