ULTRASTRUCTURE AND IMMUNOHISTOCHEMISTRY OF THE EMBRYONIC TYPE OF FAT IDENTIFIED IN THE HUMAN INFANT BREAST

In this paper we describe the light and electron microscopic appearanc e of the embryonic type of fat in human infant breast, together with i mmunocytochemical findings. This fat tissue was composed of numerous c apillaries surrounded by a mixed population of undifferentiated mesenc hymal cells and preadipocytes at various stages of differentiation. Th e preadipocytes were characterised by a number of cytoplasmic processe s, varying numbers of lipid droplets, and an envelope of electron-dens e material outside the cell membrane. Immunocytochemistry showed a cha racteristic distribution of collagen type IV adjacent to and vimentin and S100 protein within the preadipocytes, This is the first report of the ultrastructure of the human mammary embryonic type of fat. The po ssible role of the embryonic type of fat in the development and growth of the human breast is discussed. (C) 1995 Wiley-Liss, Inc.