The possibility that soluble products of Schistosoma mansoni eggs might participate in the pathogenesis of hepatic fibrosis in schistosomiasis was investigated. Both crude saline extracts of eggs (soluble egg antigen [SEA]) and a partially purified SEA fraction contained activity which stimulated guinea pig and human dermal fibroblasts to proliferate in vitro, as measured by uptake of [3H]thymidine. Maximum activity was present in fractions which eluted from Sephacryl S-200 with an apparent

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... cular weight of s12,500 and in fractions which had an estimated pI 8, as determined by preparative isoelectric focusing of partially purified SEA. Activity in crude SEA was not removed by chromatography on concanavalin A-Sepharose 4B. When concanavalin A-binding glycoproteins lacking intrinsic fibroblast-stimulating activity were incubated with spleen cells from infected or uninfected mice, fibroblasts-stimulating activity was detected in the culture supematants. Thus, SEA contains two functionally distinct molecular species. One of these directly stimulates fibroblasts, whereas the other induces the release of a fibroblast-stimulating activity from lymphocytes or macrophages or both. Since these fibroblast-stimulating factors might be elaborated in the livers of infected individuals, these observations suggest a potential role of soluble schistome products in the pathogenesis of hepatic fibrosis in schistosomiasis. Although hepatic fibrosis underlies important morbidity and mortality in schistosomiasis mansoni infections, very little is known about hepatic fibrogenesis in this disease. Dunn and coworkers (2) have demonstrated that isolated hepatic egg granulomas from Schistosoma mansoni-infected mice could incorporate radiolabeled proline into collagen in vitro, presumably representing the synthetic activity of granuloma fibroblasts. Evidence accumulated in our laboratory (9, 10) indicates that these isolated egg granulomas could spontaneously elaborate soluble factors which stimulate dermal fibroblasts in vitro to proliferate and synthesize collagen. These observations suggest a potential molecular link between granuloma formation and hepatic fibrosis. We postulated that granuloma-derived fibroblast-stimulating activity might be a soluble product secreted by the chronic inflammatory cells comprising the granulomas. Indeed, such activity has also been identified in culture supematants of in vitro-stimulated lymphocytes (7) and macrophages (3, 5, 8). The additional possibility that the granuloma-derived activity originated within the schistosome egg was investigated in the studies we report here. MATERIALS AND METHODS Animals. Outbred albino female CF1 and inbred female C57BL/6 mice weighing 18 to 20 g each were obtained from Charles River Breeding Laboratories, North Wilmington, Mass. Preparatdon and fractionation of SEA. Crude soluble egg antigen (SEA) was prepared by the method of Boros and Warren (1) from eggs isolated from the livers and intestines of CF1 mice infected 7 to 8 weeks earlier by a subcutaneous injection of 200 cercariae of a Puerto Rican strain of S. mansoni. The crude preparation was dialyzed overnight against 1,000 volumes of 10 mM sodium phosphate-buffered 0.15 M saline (pH 7.4), clarified by centrifugation for 90 min at 105,000 x g, and stored frozen at -30°C. Protein concentrations were estimated by the method of Lowry et al. (4). Crude SEA was fractionated by three different methods. A 2-mg amount of crude SEA in 2 ml of 10 mM sodium phosphate-buffered 0.15 M saline was subjected to gel filtration chromatography on a calibrated column (1.5 by 90 cm) of Sephacryl S-200