Immunohistochemical localization of chondroitin sulfate in the forestomach of the sheep

The localization of chondroitin sulfate glycosaminoglycans in the forestomach mucosa was examined by use of monoclonal mouse IgMs against chondroitin sulfate (CS-56 and 2H6). Under the light microscope, immunoreactive sites were observed in subepithelial regions and around blood vessels of the rumen, reticulum and omasum. In the reticular papillae and omasal papillae, large areas of core regions also reacted with the monoclonal antibodies. The cell surfaces of fibroblasts in the core region of the epithelium were intensely stained. Under the electron microscope, heavy staining of collagen fibrils beneath the basement membrane of the mucosal epithelium was observed. In addition, products of immunoreactions were localized at the abluminal surfaces of endothelial cells, in pinocytotic vesicles and on pits of the endothelium, as well as surrounding collagen fibrils. At the core regions of reticular papillae and omasal papillae, cell surfaces, interstitial area of collagen fibrils and elastin fibers were stained. Some of the rough endoplasmic reticulum in fibroblasts was also stained. These results suggest that chondroitin sulfate in the forestomach mucosa might serve as a charge barrier in the transport of charged molecules.