Characterisation of breast stromal fibroblasts: cell surface distribution of collagen type IV, laminin and fibronectin.

A number of cells--fibroblasts, chondrocytes and osteoblasts for example--lack the conspicuous cell surface specialisation known as lamina: instead, they possess subplasmalemmal linear densities (SLDs). These have been documented ultrastructurally as having a lamina-like external component but the extent to which they resemble true lamina in terms of protein composition has not been investigated. The relationship of the external component of the SLD to true lamina was examined in this study by light microscope immunostaining, conventional transmission electron microscopy and immuno-electronmicroscopy in intralobular stromal fibroblasts. These were studied in normal peri-tumoral breast tissue in 17 patients undergoing surgery for breast lesions. For ultrastructural immunostaining the indirect immunoperoxidase procedure was used on cryostat sections followed by embedding in epoxy resin. To varying degrees, collagen type IV, laminin and fibronectin antibodies stained fibroblasts and macrophages at the light microscope level. Using immuno-electronmicroscopy, all three antibodies localised as foci on fibroblast and macrophage surfaces. These occurred with a frequency comparable to that of SLDs as seen in non-immunostaining ultrathin sections. These observations represent a first attempt to define the protein composition of SLDs in fibroblasts in vivo. They provide an opportunity of comparing these structures with true lamina and form a basis for understanding how fibroblasts interact with their environment.