Immunohistochemical identification of the uncoupling protein in human hibernoma

The expression of the uncoupling protein (UCP), a protein unique to brown adipocyte mitochondria, was studied in sections of a human hibernoma by means of immunohistochemistry. Multilocular, but not unilocular, adipocytes expressed the UCP in the tissue. Further, the immunostaining was not uniform in multilocular cells, because small adipocytes with finely multivacuolar or scanty lipid deposit showed more intense staining. This pattern is similar to that found in brown adipose tissue. Ultrastructural investigation confirmed that a majority of proliferating cells had the morphological characteristics of brown adipocyte. Results indicate that adipocytes in hibernoma may be very close to brown adipocytes both morphologically and immunocytochemically.