Ultrastructural localization of laminin and type IV collagen in normal human breast.

The ability of carcinomas to invade and metastasize depends in part on their passage through basement membranes. Two of the major components of basement membranes are type IV collagen and laminin and these have been extensively studied by light microscopical immunocytochemical techniques to investigate alterations in their distribution in human breast carcinomas [1-3]. Breaks in the epithelial basement membrane associated with malignant epithelial tumors have been reported [3, 4]. However, these breaks are based on immunocytochemical observations and have not been correlated with basement membrane morphology. By light microscopical techniques there is no evidence of type IV collagen or laminin between myoepithelial cells or between myoepithelial and epithelial cells and they appear to be restricted to the basement membrane surrounding the entire ductule of the breast. By electron microscopy the basement membrane region contains a linear, homogeneous, electron-dense region (lamina densa) beneath a clear zone (lamina lucida) directly beneath the epithelial and myoepithelial cells of the breast ductule. These two regions constitute the basal lamina. Hemidesmosomes are present on the basal aspect of myoepithelial cells where fine filaments connect these regions to the adjacent basal lamina. The extracellular matrix components laminin and type IV collagen have both been localized in the basement membrane of the normal human breast ductule. Breaks in the continuity of these components occur in breast carcinomas and have been implicated in tumor metastasis. Using a postembedding ultrastructural immunogold technique, laminin and type IV collagen were distributed within the basal lamina surrounding the normal human breast ductule. Both components were present diffusely along the basal lamina and were not localized to particular regions, and neither were present between epithelial and myoepithelial cells. Laminin binding of these cells thus probably occurs only at the basal aspect where they are in contact with the basal lamina and is not involved in the cell-cell adhesion between epithelial and myoepithelial cells. This study provides a basis for further ultrastructural investigations of extracellular matrix components in normal and neoplastic breast tissue.