The host's genetic background determines the extent of angiogenesis induced by schistosome egg antigens

Schistosomiasis is characterised by periovular granuloma formation within the portal tract and presinusoidal venules. As inflammation wanes, continued attempts to wall off and repair hepatic injury, lead to the development of extensive fibrosis. The codependence of chronic inflammation and angiogenesis is a well-known phenomenon. Neovascularisation is a complex process of endothelial cell proliferation and remodelling of the extracellular matrix. Previous studies demonstrated the ability of schistosome soluble egg antigens (SEAs) to stimulate endothelial cell activation in vitro. In the present study, we investigated the angiogenic potential of SEA in Swiss and BALb/c mice, after infection with Schistosoma mansoni or S. haematobium and by implanting SEA-coated beads into the murine liver. Anti-CD34 and anti-Ki-67 immunohistochemical stainings demonstrated newly formed blood vessels within and at the periphery of the granulomas. However, in one third of the granulomas the pre-existing portal stroma was not destroyed by the granulomatous inflammation, angiogenesis was minimal or absent and further growth of the granuloma was prevented. In C57BL/6J and C3H/HeN inbred mice, this polarisation was even more pronounced. In 91% of the granulomas in C57BL6/J mice the portal stroma was preserved. These mice had significantly smaller granulomas, less fibrosis and less mortality as compared to the high pathology C3H/HeN mice, where 87% of the granulomas were of the angiogenic type with destruction of the pre-existing stroma, leading to more severe chronic pathology. Thus, host's genetic mechanisms regulating the degree of angiogenesis and fibrosis, determine the severity of schistosome-induced pathology.