Patogenesis of pipe-stem fibrosis of the liver (experimental observation on murine Schistosomiasis)

Mice infected with 30 cercariae of Schistosoma mansoni developed portal and septal fibrosis due to the massive and concentrated deposition of eggs in the periportal areas which occurred following the 16th week after infection. The lesion resembled pipe-stem fibrosis seen in human hepatosplenic schistosomiasis in the following characters: portal fibrosis interconnecting portal spaces as well as portal spaces and central canals; portal inflammation; periovular granulomas; vascular obstruction and telangiectasia. The liver parenchyma maintained its normal architecture. Vascular injection techniques with Indian ink and vinylite revealed that the portal system developed numerous dilated collateral venules coming from the large and medium-sized portal branches, about 10 weeks after schistosome infection. The lodging of schistosome eggs into these collaterals resulted in granulomatous inflammation and fibrosis along all the portal tracts, thus forming the pipe-stem lesion. Although not readily demonstrable grossly, the pipe-stem fibrosis of murine schistosomiasis has many similarities with the human lesion and can be considered to have the same basic pathogenesis.

An Experimental Approach to the Pathogenesis of "Pipestem" Fibrosis (Symmers' Fibrosis of the Liver)

Pathogenesis of schistosomal hepatic fibrosis ("pipestem" fibrosis of the liver) was investigated by means of the murine model. Although worm load appears as the main pathogenetic factor, alone it is not sufficient to produce that characteristic lesion. By comparing the findings in animals with heavy and prolonged Schistosoma mansoni infection, which developed or not" pipestem" fibrosis, it was observed that the lesion was more frequent in intact animals than in the splenectomized one. However, the size of the spleen, the number of recovered worms, the number of eggs per gram of liver tissue, the level of serum idiotype and anti-idiotype antibodies, the size and volume of periovular granulomas formed in the liver, all that failed to show statistically significant differences between the two groups. After analysing all these data, other factors, that apparently have been hitherto negleted, rested to explain the findings. Among them, the timing and sequence of the egg-induced intrahepatic vascular changes seemed crucial. The sequential development of intrahepatic portal vein obstruction, followed by the opening of periportal collateral veins and the continous arrival of schistosome eggs going to be lodged into the latter, appeared as essential steps in the pathogenesis of "pipestem" fibrosis

Myofibroblasts in Schistosomal Portal Fibrosis of Man

Myofibroblasts, cells with intermediate features between smooth muscle cells and fibroblasts, have been described as an important cellular component of schistosomal portal fibrosis. The origin, distribution and fate of myofibroblasts were investigated by means of light, fluorescent, immunoenzymatic and ultrastructural techniques in wedge liver biopsies from 68 patients with the hepatosplenic form of schistosomiasis. Results demonstrated that the presence of myofibroblasts varied considerably from case to case and was always related to smooth muscle cell dispersion, which occurred around medium-sized damaged portal vein branches. By sequential observation of several cases, it was evident that myofibroblasts derived by differentiation of vascular smooth muscle and gradually tended to disappear, some of them further differentiating into fibroblasts. Thus, in schistosomal pipestem fibrosis myofibroblasts appear as transient cells, focally accumulated around damaged portal vein branches, and do not seem to have by themselves any important participation in the pathogenesis of hepatosplenic schistosomiasis.

Liver morphology with emphasis on bile ducts changes and survival analysis in mice submitted to multiple Schistosoma mansoni infections and chemotherapy

In an attempt to be as close as possible to the infected and treated patients of the endemic areas of schistosomiasis (S. mansoni) and in order to achieve a long period of follow-up, mice were repeatedly infected with a low number of cercariae. Survival data and histological variables such as schistosomal granuloma, portal changes, hepatocellular necrosis, hepatocellular regeneration, schistosomotic pigment, periductal fibrosis and chiefly bile ducts changes were analysed in the infected treated and non treated mice. Oxamniquine chemotherapy in repeatedly infected mice prolonged survival significantly when compared to non-treated animals (chi-square 9.24, p = 0.0024), thus confirming previous results with a similar experimental model but with a shorter term follow-up. Furthermore, mortality decreased rapidly after treatment suggesting an abrupt reduction in the severity of hepatic lesions. A morphological and immunohistochemical study of the liver was carried out. Portal fibrosis, with a pattern resembling human Symmers fibrosis was present at a late phase in the infected animals. Bile duct lesions were quite close to those described in human Mansonian schistosomiasis. Schistosomal antigen was observed in one isolated altered bile duct cell. The pathogenesis of the bile duct changes and its relation to the parasite infection and/or their antigens are discussed.

Pathology of periportal fibrosis involution in human schistosomiasis

Optical and electron microscopical evidences of focal matrix degradation were frequently seen in liver sections of periportal fibrosis caused by schistosomiasis mansoni in man. The material came from 14 wedge hepatic biopsies taken from patients with chronic advanced hepatosplenic disease and undergoing operations for the relief of portal hypertension. Besides the presence of focal areas of rarefaction, fragmentation and dispersion of collagen fibers, the enlarged portal spaces also showed hyperplasia of elastic tissue and disarray of smooth muscle fibers following destruction of portal vein branches. Eggs were scanty in the tissue sections, and matrix degradation probably represented involuting changes related to the progressive diminution of parasite-related aggression, which occurs spontaneously with age or after cure by chemotherapy. The changes indicative of matrix degradation now described are probably the basic morphological counterpart of periportal fibrosis involution currently being documented by ultrasonography in hepatosplenic patients submitted to curative chemotherapy.

Production of septal fibrosis of the liver by means of foreign protein injections into rats

Similarities and differences in antigenic humoral responses and electrophoretic patterns between Capillaria hepatica and pig-serum were investigated as a contribution to the understanding of hepatic fibrosis induced by the parenteral administration of foreign proteins. Only two out of 10 rats receiving repeated intraperitoneal injections of an extract of Capillaria hepatica-infected mouse liver presented septal hepatic fibrosis (20%). Under the same experimental conditions, 4 out of 9 rats (44.4%) developed septal fibrosis following whole pig-serum administration. Injections of normal mouse liver extracts did not result in hepatic fibrosis. Since a 100% septal fibrosis rate is observed in experimentally Capillaria hepatica-infected rats, it appeared that Capillaria hepatica products continuously released from inside the liver creates a much more effective fibrosis inducing mechanism than the parenteral administration of such factors. Thus, repeated peritoneal administration of a foreign protein to rats would not reveal the full fibrogenic potential it may have under natural conditions.

Capillaria hepatica-induced hepatic fibrosis in rats: paradoxical effect of repeated infections

Multiple exposures to parasitic agents are considered an important factor in the genesis of the most severe forms of the diseases they cause. Capillaria hepatica-induced septal fibrosis of the liver in rats usually runs without signs of portal hypertension or hepatic failure. After determining the hepatic profile of 15 animals during the course of a single infection, we submitted 20 rats to multiple Capillaria hepatica infections to determine whether repeated exposures would augment fibrosis production, transforming septal hepatic fibrosis into a true cirrhosis. Ten single-infection rats served as controls. A total of 5 exposures, with 45-day intervals, were made. Histological changes were followed by means of surgical liver biopsies, collected prior to infection and to each re-infection. Functional changes were minimal and transient. Although a slight recrudescence of fibrosis was observed after the first two re-infections and when the single-infected control group was re-infected at the end of the experiment, subsequent re-infections failed to increase the amount of fibrosis. On the contrary, there occurred quantitative and qualitative evidence of collagen degradation and suppression of parasite development. These paradoxical results are in keeping with the hypothesis that a complex immunological modulation participates in the mechanism of hepatic fibrosis induced by Capillaria hepatica infection in rats.

Capillaria hepatica-induced septal fibrosis in rats: a contribution to the study of liver fibrogenesis

INTRODUCTION: Septal fibrosis of the liver regularly develops in rats infected with the nematode Capillaria hepatica. Curative treatment of the infection prevents the development of septal fibrosis when intervention occurs up to postinfection day (PID) 15, but not later. The present investigation aimed to demonstrate which parasitic factors are present when the process of septal fibrosis can no longer be prevented by curative treatment. METHODS: Wistar rats were infected with 600 embryonated eggs of C. hepatica administered by gavage and treated with ivermectin and mebendazole in separate groups at PIDs 10, 12, 15, 17 or 20. Rats from each group and their nontreated controls, were killed and examined 40 days after the end of treatment. RESULTS: Findings by PID 15 were compatible with the stage of complete maturation of infection, when worms and eggs were fully developed and a complex host-parasite multifocal necroinflammatory reaction showed greater intensity, but with no signs of septal fibrosis, which appeared from PID 17 onward. CONCLUSIONS: Since the worms spontaneously died by PID 15, not only septal fibrosis production, but also its maintenance and further development appeared dependent on the presence of eggs, which were the only parasitic factor remaining thereafter.

Hyperplasia of elastic tissue in hepatic schistosomal fibrosis

Elastic tissue hyperplasia, revealed by means of histological, immunocytochemical and ultrastructural methods, appeared as a prominent change in surgical liver biopsies taken from 61 patients with schistosomal periportal and septal fibrosis. Such hyperplasia was absent in ecperimental murine schistosomiasis, including mice with "pipe-stem" fibrosis. Displaced connective tissue cells in periportal areas, such as smooth muscle cells, more frequently observed in human material, could be the site of excessive elastin synthesis, and could explain the differences observed in human and experimental materials. Elastic tissue, sometimes represented by its microfibrillar components, also appeared to be more condensed in areas of matrix (collagen) degradation, suggesting a participation of this tissue in the remodelling of the extracellular matrix. By its rectratile properties elastic tissue hyperplasia in hepatic schistosomiasis can cause vascular narrowing and thus play a role in the pathogenesis of portal hypeertension.

Capillaria hepatica: a cause of septal fibrosis of the liver

Fine, long, fibrous septa were observed as a late change developing in the acinar zone III of the liver of rats experimentally infected with the helminth Capillaria hepatica. Hepatic septal fibrosis begun 30 days after inoculation of embryonated eggs into the stomach of rats and became clearly evident from the 40th day onwards. Experimental observation was undertaken for 170 days. Septal fibrosis increased progressively with time and was most marked when the parasitic nodules formed around larvae, disintegrating worms and eggs were involving. Septal fibrosis of the liver has not been previously recognized as a manifestation of hepatic capillariasis. The presence of sequestered parasite antigens, probably being slowly released within the liver, appears to be a major factor in the pathogenesis of hepatic septal fibrosis observed in rats with C. hepatica infection.

The use and limitations of ultrasonography in the diagnosis of liver morbidity attributable to Schistosoma mansoni infection in community-based surveys

The objective of this population-based study was to estimate the liver morbidity attributable to Schistosoma mansoni infection by ultrasonography adopting the proposed standard protocols of the Cairo Meeting on Ultrasonography, 1991. We examined 2384 individuals representing 20 of the households of the rural population of the Ismailia Governorate, East of Delta, Egypt. Prevalence of S. mansoni and S. haematobium infections were 40.3 and 1.7 respectively. Portal tract thickening (PTT) grade 1, 2 and 3 considered diagnostic of schistosomal liver morbidity was detected in 35.1, 1.3 and 0.2 individuals respectively. Generally, ultrasonographically-detected pathological changes increased with age, but correlated with intensity of infection only in age group 20-59 years. Comparing individuals with and without S. mansoni infections in an endemic and a non-endemic community indicated no significant difference between the former and the latter in either case. In conclusion: ultrasonography had a limited value in estimating schistosomal liver morbidity in our population-based study where early grades of liver morbidly were prevalent. The criteria of diagnosing grade I portal fibrosis need to be revised as well as the staging system proposed by the Cairo Meeting on ultrasonography in schistosomiasis.

Calomys callosus: an alternative model to study fibrosis in Schistosomiasis mansoni: the pathology of the acute phase

Twenty Calomys callosus, Rengger, 1830 (Rodentia-Cricetidae) were studied in the early stage of the acute schistosomal mansoni infection (42nd day). The same number of Swiss Webster mice were used as a comparative standard. Liver and intestinal sections, fixed in formalin-Millonig and embedded in paraffin, were stained with hematoxilin and eosin, PAS-Alcian Blue, pH = 1.0 and 2.5, Lennert's Giemsa, Picrosirius plus polarization microscopy, Periodic acid methanamine silver, Gomori's silver reticulin and resorcin-fuchsin. Immunohistological study (indirect immunofluorescence and peroxidase labeled extravidin-biotin methods) was done with antibodies specific to pro-collagen III, fibronectin, elastin, condroitin-sulfate, tenascin, alpha smooth muscle actin, vimentin and desmin. The hepatic granulomas were small, reaching only 27 of the volume of the hepatic Swiss Webster granuloma. They were composed mainly by large immature macrophages, often filled by schistosomal pigment, characterizing an exsudative-macrophage granuloma type. The granulomas were situated in the parenchyma and in the portal space. They were often intravascular, poor of extracellular matrix components, except fibronectin and presented, sometimes alpha smooth muscle actin and vimentin positive cells. The C. callosus intestinal granulomas were similar to Swiss Webster, showing predominance of macrophages. Therefore, the C. callosus acquire very well the Schistosoma mansoni infection, without developing strong hepatic acute granulomatous reaction, suggesting lack of histopathological signs of hypersensitivity.

Effect of interferon-alpha on experimental septal fibrosis of the liver - study with a new model

Interferon-alpha is used in antiviral therapy in humans, mainly for viral hepatitis B and C. An anti-fibrotic effect of interferon has been postulated even in the absence of anti-viral response, which suggests that interferon directly inhibits fibrogenesis. Rats infected with the helminth Capillaria hepatica regularly develop diffuse septal fibrosis of the liver, which terminates in cirrhosis 40 days after inoculation. The aim of this study was to test the anti-fibrotic effect of interferon in this experimental model. Evaluation of fibrosis was made by three separate methods: semi-quantitative histology, computerized morphometry and hydroxyproline measurements. Treatment with interferon-alpha proved to inhibit the development of fibrosis in this model, especially when doses of 500,000 and 800,000 IU were used for 60 days. Besides confirming the anti-fibrotic potential of interferon-alpha on a non-viral new experimental model of hepatic fibrosis, a clear-cut dose-dependent effect was observed.

Worm load and septal fibrosis of the liver in Capillaria hepatica-infected rats

Inocula, varying from 15 to 1,000 embryonated Capillaria hepatica eggs, were administered to young adult rats by gastric tube, in an attempt to investigate the influence of worm load in the production of septal fibrosis of the liver. Low doses of 15, 30 or 50 eggs were sufficient to produce septal fibrosis, but it appeared with variable degrees of intensity and always with focal distribution. Septal fibrosis became diffuse, progressive with time, and already well developed 40 days after infection, when 100 eggs or more were administered. However, higher inocula (200, 500 and 1,000 eggs) did not intensify septal fibrosis, although the number of parasitic focal lesions proportionally augmented.

Immunological tolerance to pig-serum partially inhibits the formation of septal fibrosis of the liver in Capillaria hepatica-infected rats

Systhematized septal fibrosis of the liver can be induced in rats either by repeated intraperitoneal injections of pig-serum or by Capillaria hepatica infection. The relationship between these two etiological factors, as far as hepatic fibrosis is concerned, is not known, and present investigation attempts to investigate it. C. hepatica-induced septal fibrosis of the liver was considerably inhibited in rats previously rendered tolerant to pig-serum. Pig-serum-tolerant rats developed antibodies against pig-serum when infected with C. hepatica, but this did not happen when the infection occurred in normal rats. On the other hand, anti-C. hepatica antibodies failed to recognize any epitope in pig-serum, by Western blot. However, no evidence of an immunological cross reactivity was found, at least at the humoral level. Alternatively, cell-mediated mechanisms may be involved, and further investigations are warranted.