Ultrastructural and immunohistochemical studies of intralobular fibroblasts in human submandibular gland: the recognition of a 'CD34 positive reticular network' connected by gap junctions.

In order to clarify the ultrastructural and immunophenotypic characteristics of intralobular stromal cells in the human submandibular gland, normal tissues were examined from 25 patients by conventional histology of wax sections, light microscope immunohistochemistry, conventional thin-sectioning transmission electron microscopy, immuno-electronmicroscopy (for the CD34 antigen) and scanning electron microscopy. Spindled stromal cells had abundant rough endoplasmic reticulum cisternae typical of fibroblasts. Some actin filaments and microtubules were seen, but the filaments lacked the focal densities of smooth-muscle, nor was a lamina present. Fibroblasts exhibited long slender processes which associated with other fibroblasts by means of gap junctions and with mononuclear cells (lymphocytes, plasma cells, macrophages) by means of close appositions of membrane. Immunoelectron microscopy for CD34 revealed positive staining over the fibroblast surfaces but not over the mononuclear cells. The novel observation of gap junctions suggests a tissue closely organized as a network in physical and perhaps physiological terms. This network also incorporates mononuclear cells. The possible role in immunosurveillance of this CD34-positive reticular network is discussed.