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Transcriptomics of Schistosoma japonicum-induced immunopathology

Schistosomiasis continues to be an important cause of parasitic morbidity and mortality world-wide. Determining the molecular mechanisms regulating the development of schistosome-induced pathology, including granuloma formation, fibrosis and splenomegaly, is essential for understanding how schistosomes influence the immune system of the mammalian host. I report on the first whole genome microarray analysis of the murine liver and spleen during the progression of Schistosoma japonicum infection and of S. japonicum-Soluble Egg Antigen (SEA)-stimulated macrophages. My analyses of the infected liver revealed a distinct temporal relationship between the expression of chemokines and the recruitment of cells to the liver. T-cell and B-cell chemoattractants were up-regulated earlier reflecting the recruitment of these cells to the liver as illustrated by flow cytometry. The later phases of the response corresponded with peak accumulation of eosinophils, neutrophils, macrophages and myofibroblasts/hepatic stellate cells (HSCs) and the expression of chemokines with activity for these cells including CCL11, members of the Monocyte-chemoattractant protein family (CCL7, CCL8, CCL12) and the hepatic stellate cell/myofibroblast chemoattractant CXCL1. Peak expression of macrophage chemoattractants (CCL6, CXCL14) and markers of alternatively-activated macrophages (e.g. Retnla) during this later phase provided further evidence for a role for these cells in schistosome-induced pathology. Additionally, I demonstrated that CCL7 immunolocalises to the fibrotic zone of granulomas. Furthermore, striking up-regulation of neutrophil markers and the localisation of neutrophils and the neutrophil chemokine S100A8 to fibrotic areas suggested the involvement of neutrophils in S. japonicum¬-induced hepatic fibrosis. The transcriptional profile of the spleen was closely related to changes in cellular composition illustrated by flow cytometry and immunohistochemistry. Significant up-regulation of genes associated with progression through the cell cycle, proliferation makers and genes involved in lymphocyte proliferation, paralleled the initial expansion of T-cells and B-cells and the increased cellularity of the spleen overtime. Accumulation of eosinophils, neutrophils and macrophages was paralleled by enhanced expression of markers for these cells and the declining proportion of B- and T-cells in the spleen over time was reflected in the decreased expression of B- and T-cell markers. Significant up-regulation of Chi3l3 and F4/80+ macrophages suggested the presence of alternatively activated macrophages in the spleen, where these cells could play an immunoregulatory role. Comparison of the liver and spleen profiles revealed divergent expression of chemokines and cell adhesion molecules. Expression of lymphocyte chemokines including the homeostatic chemokines, CXCL13, CCL19 and CCL21, were significantly up-regulated in the liver while down regulated in the spleen. Expression of chemokines with activity for eosinophils (CCL11, CCL24), neutrophils (CXCL1) and monocytes (CXCL14, CCL12) and the cell adhesion molecules VCAM1, NCAM1, PECAM1 were up-regulated in the liver while unchanged in the spleen. Chemokines up-regulated in both organs were expressed at significantly higher levels in the liver. Divergent expression of chemokines and cell adhesion molecules likely contributes to the development of a chemotactic signalling gradient that promotes recruitment of effector cells to the liver. The results of liver and spleen microarrays suggested an important role for alternatively activated macrophages in the development of schistosome-induced pathology. This led me to investigate the in vivo transcriptional profile of S. japonicum SEA-stimulated peritoneal macrophages. The transcriptional profile of these cells was characterised by up-regulation of alternatively activated macrophage makers (Chi3l3, Chi3l4, Arg1). Retnla was not significantly induced in these macrophages suggesting that the specific function of these cells may differ to those induced by S. mansoni and other parasites. Other features of the transcriptional profile of these cells included modulated expression of T-cell co-stimulatory molecules and chemokines which may confer immunomodulatory activity. S. japonicum-stimulated alternative activation of macrophages was additionally associated with deactivation of classical activation pathways and altered expression of cell surface receptors and complement components that may alter phagocytic activity. Together these data significantly enhance our understanding of the mechanisms associated with alternative activation of macrophages and provide significant insight into the role of these cells in schistosomiasis japonica. The findings presented in this thesis represent the most comprehensive description to date of the molecular mechanisms, and especially chemotactic signalling pathways, regulating the development of schistosome-induced granulomas, fibrosis, splenomegaly and alternative macrophage activation in the murine host. In summary, my data have revealed that co-ordinated gene expression of chemokines in the liver and spleen regulates the recruitment of cells to the liver during schistosome infection. My results provide additional evidence for a role for neutrophils and alternatively activated macrophages in the development of schistosome-induced pathology and provide further insight to the molecular basis of alternative macrophage activation during infection. Furthermore, my data serve to highlight clear differences in the pathogenesis of schistosomiasis mansoni and schistosomiasis japonica. Together these findings further our understanding of the systemic, local, cellular, and especially, chemokine signalling pathways that regulate the development of S. japonicum-induced pathology and offer correlative insight into the pathogenesis of other chronic inflammatory diseases where fibrosis, splenomegaly and alternative activation of macrophages are common features.