Copyright © American Association of Pathologists Morphology ofChronic Collagen Resorption A Study on the Late Stages ofSchistosomal

Hepatic periovular schistosomal granulomas produced in mice with SO cercariae per 10 weeks of infection were seen to involute following curative treatment of schistosomiasis. Residual scars remained, however, and the collagen tissue in them presented morphologic evidence of a slow, progressive degradation that lead to the almost complete disappearance ofthe lesions 4.5 months after chemotherapy. Ultrastructural changes indicative ofcollagen degradationwere representedby focal lytic dissolution ofcollagen fibrils and/or by the transformation ofmch fibrils into a granular electron dense materiaL a picture different from that seen in more acute models ofco n resorption. In older, in-voluting granulomas, both type I and HI collagens were found up to the end ofthe resorption process. The immunolluorescence staining for procollagen m and fibronectin correlated with collagen synthesis and the THE SCHISTOSOMAL periovular granuloma is an essentially fibrogenic lesion. As a model, the schisto-somal granuloma has been used to identify the soluble factors involved in fibroblast stimulation and collagen synthesis,1 to study the sequence of deposition of ge-netically different types of collagens,2 and to investi-gate the pathogenesis of pipe-stem fibrosis of the liver.34 The morphology of collagen formation and degradation has also been explored with this model.5 It has been demonstrated that, soon after curative treatment ofschistosomiasis, hepatic periovular gran-ulomas start to involute. They then present an ultra-structural composite picture of fibroblast hyperplasia plus extraceliular collagen breakdown and internal-ization or phagocytosis ofcollagen fragments by mac-rophages, fibroblasts, and myofibroblasts.5 The sequential morphologic changes seen in invo-luting periovular granuloma are similar therefore to those observed in other models, such as during the in