Regulation of Fibroblast Functions by Products of Schistosomal Egg Granulomas: Potential Role in the Pathogenesis of Hepatic Fibrosis

Tumourigenic effect of Schistosoma haematobium total antigen in mammalian cells

Schistosoma haematobium is endemic in several regions of Africa and has been shown to be associated with predominantly squamous cell bladder carcinoma. The mechanisms underlying the association between S. haematobium and bladder squamous cell carcinoma is largely unknown. All the reports so far, demonstrate exclusively an epidemiological evidence linking S. haematobium infection with squamous cell bladder carcinoma. We hypothesized that these parasite antigens might induce tumourigenesis. For this, we used normal mammalian cells of Chinese hamster ovary (CHO) and treated the cells in culture with S. haematobium total antigen (Sh). Our results showed increased proliferation in Sh-treated cells in comparison with the controls. The CHO cells exposed to Sh were inoculated subcutaneously into male nude mice and formed sarcomas (n = 5/5). The cells from the sarcomas expressed vimentin filaments and were negative to cytokeratin. Our results demonstrate for the first time that S. haematobium antigens induce tumour development in nude mice.

Host immune factors regulating fibrosis

Mononuclear cells produce lymphokines and monokines, the function of which is to initiate the mobilization, proliferation and differentiation of additional mononuclear cells in an inflammatory site. In addition, these inflammatory cells produce biologically active mediators which modulate the functions of certain non-inflammatory cell targets. Lymphokines and monokines can stimulate chemotaxis, division, and matrix synthesis by connective tissue fibroblasts. Additional mononuclear cell-derived mediators can inhibit or suppress these fibroblast functions, implicating the host immune system in the regulation of connective tissue metabolism associated with an inflammatory response. Altering the balance of the production and/or release of these connective tissue-active agents could result in excess fibroblast growth and matrix synthesis (fibrosis) and its pathological manifestations.

Regulation of fibroblast proliferation by Kupffer cells and monocytes

Liver cirrhosis can be considered as an alteration of the homeostatic mechanisms that maintain cell-cell and cell-matrix interactions. The mechanisms that maintain homeostasis and, therefore, that control fibroblast proliferation and collagen synthesis, are unknown. Experiments were performed to study the role of Kupffer cells in regulating fibroblast proliferation and collagen synthesis and to study the antifibrogenic properties of colchicine. Non-parenchymal cells isolated from normal and CCl4-treated rats were cultured. The cultures from normal livers contained few fibroblasts whereas those from CCl4-treated animals contained many fibroblasts. Removal of adherent cells obtained from normal liver favoured fibroblast proliferation. The fibroblasts from normal or CCl4-treated rats were similar and contained collagens type I and type III. The results obtained suggest that normal Kupffer cells control fibroblast proliferation and that incoming monocytes stimulate fibroblast proliferation. Colchicine inhibits the entry of monocytes into the injured liver and could prevent liver fibrosis by this mechanism.

Fibrosing granulomas in the equine liver and peritoneum: a retrospective morphologic study

Fibrosing granulomas were found in the liver and occasionally on the intestinal and diaphragmatic serosae and in the lung of 11 horses submitted for necropsy. Although these granulomas were considered incidental findings in most of the horses, they had caused liver failure in 1 horse. The granulomas typically were characterized by a dense collagenous core that frequently was mineralized. The periphery contained a rim of inflammatory cells. Only in 1 of the 11 horses was there evidence of an egg shell suggestive of schistosomes. Schistosomal eggs were not detected in the feces of the horses. The typical architecture of the granulomas combined with the occasional finding of a residual egg led to the circumstantial conclusion that the fibrosing granulomas were the result of chronic schistosomiasis of undeterminable origin.

Immunopathology of Schistosoma mansoni infection

Schistosomiasis mansoni is a chronic helminthic disease that affects about 100 million people in the tropics. The worms have a life span of 5 to 10 years, and they live in the mesenteric veins of the host. Lightly infected individuals are asymptomatic or manifest mild intestinal symptoms. Heavily infected individuals often develop severe morbidity with hepatosplenomegaly, sometimes with a fatal outcome. Morbidity is attributed to the strong humoral and T-cell-mediated host immune responses developed to a variety of parasite antigens and expressed as tissue inflammations. The immunopathology includes dermatitis, immune complex-mediated kidney disease, and, chiefly, T-cell-mediated granuloma formation and fibrosis around disseminated parasite eggs. This review describes the mechanisms of induction and expression of immunopathology in infected persons and experimental animals. Immunoregulatory mechanisms that modulate the enhanced immune responses and may ameliorate excessive morbidity are discussed.

Schistosomal egg granuloma-derived fibroblast-stimulating factor is apparently distinct from interleukin-1

We have previously reported that egg granulomas isolated from livers of Schistosoma mansoni-infected euthymic mice in vitro elaborate a factor(s) that stimulates a variety of fibroblast responses including fibroblast proliferation and enhanced synthesis of extracellular matrix proteins. We have postulated that these factors play a role in the pathogenesis of hepatic fibrosis in schistosomiasis mansoni. Serum-free supernatants from egg granuloma cultures also stimulate thymocyte proliferation in an assay that defects interleukin-1 (IL-1). Thymocytes and fibroblasts are stimulated to proliferate by the same fractions of egg granuloma culture supernatant separated by gel filtration, isoelectric focusing, and ion-exchange chromatography. This suggested that granuloma-derived IL-1 is responsible for the observed fibroblast stimulation. Here we report that the ability of granuloma culture supernatants to stimulate the IL-1-sensitive D10.G4.1 cells but not fibroblasts is removed by treatment with immobilized anti-IL-1 antibody. We also observed that dialyzed culture supernatants from egg granulomas obtained from infected congenitally athymic (nude) mice also stimulate fibroblast proliferation. Treatment with anti-IL-1 antibody did not abrogate this response. In contrast to our experience with egg granulomas isolated from euthymic mice, IL-1- and fibroblast-stimulating activity could be separated by gel filtration and isoelectric focusing. We conclude that the fibroblast growth-stimulating activities elaborated by egg granulomas from S. mansoni-infected euthymic and athymic mice may be different but both appear to be distinct from IL-1.