Hepatic granulomas induced by glucan. An ultrastructural and peroxidase-cytochemical study

Granulomas were induced in rat liver by the injection of glucan, a beta-1,30-polyglucose with an activating effect on macrophages. The livers were fixed by perfusion with glutaraldehyde and processed for cytochemical localization of peroxidase (PO) as well as for scanning and transmission electron microscopy. By light microscopy the granulomas appeared as spherical cell clusters located throughout the liver parenchyma. They exhibited strong PO activity at the periphery with weak to negative reaction at the center. Most granulomas were in direct continuity with adjacent sinusoids. Morphometry revealed that the volume of granulomas increased to about 10 per cent of the total parenchymal volume at 10 days after glucan treatment, decreasing to less than 2% at 90 days. By scanning electron microscopy most cells at the periphery of granulomas were covered with numerous blebs and ruffles, the typical surface features of activated macrophages. By transmission electron microscopy the typical granulomas consisted of mononuclear phagocytes, giant cells, and a few lymphocytes. The phagocytes, as identified by phagocytosis of glucan, exhibited three distinct PO patterns: (1) strong PO activity in the nuclear envelope and endoplasmic reticulum with no activity in cytoplasmic granules; (2) weak or absent reaction in nuclear envelope and endoplasmic reticulum with no PO-positive granules in cytoplasm; and (3) absent reaction in nuclear envelope and endoplasmic reticulum but with a few strongly stained cytoplasmic granules. The first cell type, resembling Kupffer cells, was found mainly at the granuloma periphery. The second cell type, identified ultrastructurally as epithelioid cells, and the third cell type, with PO features of monocytes, were found mainly in the center of granulomas. The multinucleated giant cells which were also present in the center of granulomas exhibited weak to negative PO reaction in nuclear envelope and endoplasmic reticulum and contained large numbers of glucan particles. These observations suggest that most cells in the center of the granulomas, including the giant cells, are derived from blood monocytes. The mononuclear phagocytes at the periphery, on the other hand, seem to be for the most part former Kupffer cells.