Human macrophage-mediated cytotoxicity of Schistosoma mansoni. Functional and structural features of the effector cells.

Human monocytes were purified from peripheral blood and cultured in vitro on hydrophobic membranes. Such cells developed into mature tissue-type macrophages after approximately 1 week in culture. During this maturation period the macrophages developed a potent cytotoxic mechanism whereby they could kill the schistosomula of Schistosoma mansoni in standard in vitro cytotoxicity assays. Cytological and ultrastructural studies of the cells grown in vitro indicated that macrophages developed many of the classical histological and ultrastructural features of 'activated' cells with ruffled plasma membranes and significant increases in rough endoplasmic reticulum and Golgi vesicles. Effective cytotoxicity depended upon contact of the effector cells and their parasite target. Further, experiments using metabolic inhibitors indicated that cytotoxicity was dependent upon protein synthesis. Initial results point to the macrophage factor being distinct from some of the better-characterised macrophage secretory products such as tumour necrosis factor, proteases and products of oxygen metabolism.