ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL OBSERVATIONS ON INTRALOBULAR FIBROBLASTS OF HUMAN BREAST, WITH OBSERVATIONS ON THE CD34 ANTIGEN

Understanding the diverse pathological processes which are initiated i n the ultimate organizational units of the mammary parenchyma - the lo bules and ductules - will to a large extent be based on understanding the normal breast. During the routine diagnostic evaluation of 11 surg ical specimens for a variety of benign and malignant breast lesions, g rossly normal mammary parenchyma, subsequently confirmed as histologic ally normal by light microscopy, was sampled for this purpose. Tissue was studied by histology, light microscope immunohistochemistry, trans mission electron microscopy, scanning electron microscopy, and ultrast ructural immunohistochemistry. A number of features hitherto disregard ed in the literature are described in detail, or are elaborated with r espect to earlier descriptions. These include: the presence of solitar y cilia and lipid-rich residual bodies in intralobular fibroblasts, an d the frequent association of inflammatory cells (lymphocytes, plasma cells, macrophages, mast cells) with the cell bodies and processes of fibroblasts. For the first time also, CD34, best known as an endotheli al cell marker, has been demonstrated by ultrastructural immunohistoch emistry on the cell surface of fibroblasts. Finally, scanning electron microscopy has demonstrated new features of the intercellular matrix in which the fibroblasts and inflammatory cells are located. The signi ficance of these findings is discussed in terms of a postulated immune surveillance role of the mononuclear cells in collaboration with the fibroblasts.