Desmin is a smooth muscle protein consisting of intermediate filaments. It is also present in other cell types. We obtained desmin antibodies from New Zealand white rabbits which were immunized with desmin following its extraction from chicken gizzard smooth muscle. By immunocytochemical methods, the antibody stained the Z-line of rat skeletal myofibrils and produced only one band with chicken gizzard desmin by immunoblotting. The antibody was specific for desmin, but was not tissue-specific. Wistar rat liver was studied by indirect immunoperoxidase and immunofluorescent methods using the antibody. Cells which reacted were diffusely distributed in the hepatic lobule, had stellate shape, bore elongated cytoplasmic extensions and contained few fat droplets. The fat droplets increased in size and amount after administration of vitamin A, and contained vitamin A as determined by ultraviolet exposure and gold impregnation. The fat-containing cells did not phagocytose carbon particles after injection of colloidal carbon and were, therefore, classified as fat-storing cells (Ito cells).

The reticular meshwork of the rat spleen, which consists of both fibrous and cellular reticula, was investigated by transmission electron microscopy. The fibrous reticulum of the splenic pulp is composed of reticular fibers and basement membranes of the sinuses. These reticular fibers and basement membranes are continuous with each other. The reticular fibers are enfolded by reticular cells and are composed of two basic elements: 1) peripheral basal laminae of the reticular cells, and 2) central connective tissue spaces in which microfibrils, collagenous fibrils, elastic fibers, and unmyelinated adrenergic nerve fibers are present. The basement membranes of the sinuses are sandwiched between reticular cells and sinus endothelial cells and are composed of lamina-densalike material, microfibrils, collagenous fibrils, and elastic fibers. The presence of these connective tissue fibrous components indicates that there are connective tissue spaces in these basement membranes. The basement membrane is divided into three parts: the basal lamina of the reticular cell, the connective tissue space, and the basal lamina of the sinus endothelial cell. When the connective tissue space is very small or absent, the two basal laminae may fuse to form a single, thick basement membrane of the splenic sinus wall. The fibrous reticulum having these structures is responsible for support (collagenous fibrils) and rebounding (elastic fibers). The cells of the cellular reticulum--reticular cells and their cytoplasmic processes, which possess abundant contractile microfilaments, dense bodies, hemidesmosomes, basal laminae, and a well-developed, rough-surfaced endoplasmic reticulum, and Golgi complexes, which are characteristic of both fibroblasts and smooth muscle cells--are considered to be myofibroblasts. They may play roles in splenic contraction and in fibrogenesis of the fibrous reticulum. The contractile ability may be influenced by the unmyelinated adrenergic nerve fibers that pass through the reticular fibers. The three-dimensional reticular meshwork of the spleen consists of sustentacular fibrous reticulum and contractile myofibroblastic cellular reticulum. This meshwork not only supports the organ but also contributes to a contractile mechanism in circulation regulation, in collaboration with major contractile elements in the capsulo-trabecular system.

Weinvestigatedthe specificity of various autoantibodies in antimitochondrial antibody (AMA)-negative patients with primary biliary cirrhosis (PBC). Weexamined sera from 144 patients with PBC, 17 of whomwere AMAnegative by indirect immunofluorescence. The AMAnegative group showed a significantly higher positivity for smooth muscle antibody, but not for antinuclear antibody, as compared with the AMA-positive group. IgG class anti-PDH by enzymelinked immunosorbent assay (ELISA) were detected in 13 % of the AMA-negative group. However, all PBC patients showed positive IgG, IgA, and/or IgM class anti-M2 to the four M2 proteins by immunoblotting. These results suggest that the detection of IgG and IgMclass anti-PDH and that of antibodies to the four M2proteins increases the positivity of this ELISA method, and that detection ofIgG, IgA, and IgM class anti-M2 to the four M2 proteins by immunoblotting is useful in diagnosing AMA-negative patients with PBC. (Internal Medicine 34: 496-501, 1995)

Ito cells (FSC) have been thought to be collagen-producing cells with regard to hepatic fibrosis. We have found that desmin, a structural protein of muscular intermediate filaments, is found in the cytoplasm of FSC, even in negative vitamin Aautofluorescence FSC, by using immunocytochemical techniques. In the present study, numbers of FSC produced by the administration of heterogeneic serum or carbon tetrachloride were detected in fibrous and non-fibrous areas of hepatic lobules by using a morphometrical analyser. After 8 weeks of intraperitoneal injections of heterogeneic serum into rats, FSC in fibrous septa increased in number and the increase continued to 12 weeksalthough the numbers of FSC in non-fibrous areas and in controls given homologous serum did not change during the experiment. In the case of rats administered CCL once, FSC in fibrous areas increased in numbers after 48 h through 72 h, although the number of FSC in non-fibrous areas and in controls did not change. The results, with an apparent increase in numbers of FSC in fibrous areas and no change in non-fibrous areas, showed the possibility of hyperplasia due to cell division of FSC in the new fibroplastic areas.

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