Cellular constituent and intercellular adhesion in Schistosoma mansoni granuloma: an ultrastructural study

The present work deals with the structural analysis of Schistosoma mansoni granuloma and the visualization of cellular interaction at an ultrastuctural level in the acute (8 weeks) and chronic (20 weeks) stages of infection, for more detailed understanding of pathophysiology of the disease. Although, S. mansoni granuloma is mediated by T-lymphocytes, yet in this work the macrophage cells and not the lymphocytes represented the main cell type in cellular and fibrocellular granulomas. The cellular and fibrocellular granulomas detected in the acute stage of infection elicited no difference in cellular constituent to those of the chronic stage respectively. Macrophage cells and fibrocytes were the only cell type detected in fibrotic granuloma. The monocytes may be considered the first cell reaching the site of the trapped egg as they formed the first row of cells around the egg. The cellular infiltrate forming the granuloma: monocytes, macrophages, lymphocytes, eosinophils, fibroblasts and plasma cells revealed direct contact or adherence between them and even between the individual cell type, through extending protrusion from the cell membrane of adjacent cells. They constituted an integrated network which encircled the egg. Similar adhesion between inflammatory cells in the blood vessels and between the inflammatory cells and the endothelial cells were displayed. These points of intercellular adhesion appeared as if, not only used for functional communication between the cells, but also for cellular deplacement either in the extracellular matrix or in the blood stream until extravasation. In conclusion, S. mansoni granuloma is a highly organized cellular lesion, in which cell to cell communication occurs through direct cell contact.