Human bilharzial ureters: IV. Ultrastructural interaction between multinucleate giant cells and the parasite eggs

The ultrastructural interaction between multinucleate giant cells (MGCs) and the Schistosoma haematobium eggs is described at the transmission electron microscopy (TEM) level, in granulomas of the lower ureteral segments of Saudi patients. The MGCs were found only within the parasite empty egg-shells which were embedded in the ureter submucosa and muscularis. For the first time, two morphologically different types of MGCs were recognized: the moderate to electron-dense type I contained two types of 8-12 nuclei and cytoplasm poor in cell organelles which appeared non-functional. Type 1 MGCs were considered to be "old" and non-active cells. The electron-lucent to moderately dense type II MGCs contained 3-4 nuclei of one type, and cytoplasm rich in cell organelles. According to the performance of their organelles, type II MGCs were considered to be "young" and highly active cells. The human type II MGCs did not form the cytoplasmic membranous labyrinths previously described for the free moving MGCs obtained from experimental mice, and were suggested to be involved in the cell motility. As in murine MGCs, type II cells were incorporated in exocytic and endocytic activities aimed the degradation of the inner soft layer of the egg-shell. This study shows that individual macrophages were responsible for eliminating the outer and possibly the middle hard layers of the egg-shell.