Apoptosis of Trypanosoma musculi co-cultured with LPS activated macrophages: enhanced expression of nitric oxide synthase INF-gamma and caspase.

Trypanosoma musculi-macrophage co-cultures were studied to investigate the biological role of lipopolysaccharide (LPS) induced cytokines in controlling the proliferation of parasites in vitro. Macrophages, isolated by peritoneal lavage, sustained the growth and proliferation of the parasites. Macrophages activated with LPS were characterized by up-regulation of nitric oxide synthase (iNOS) and phagocytosis of fluorescent latex spheres. Activated macrophages showed marked inhibition of the association and proliferation of the parasites. The LPS treated macrophages produced cytokines, especially interferon gamma (INF-gamma), which was detected by Western blot. Trypanosomes, inhibited from association with macrophages, did not proliferate and instead formed clusters held together by their flagella. Cells in these clusters were apoptotic, as demonstrated by the Apoptag reaction and gel fragmentation assay. In addition, high levels of caspase 8 and caspase 3 were shown in floating trypanosome clusters. The results would suggest that INF-gamma and other cytokines released by activated macrophages, possibly functioning through the INF-gammaR1, Fas ligand, CD95 or other death ligands in the trypanosome plasma membrane initiates the apoptosis cascade in trypanosomes.

Co-culture of Trypanosoma musculi with spleen-derived adherent fibroblasts: possible transfer of small molecules via connexons.

Trypanosoma musculi, a protozoan parasite specific to mouse, was cultured in vitro in the presence of spleen-derived adherent cells. T. musculi co-cultured with adherent cells survived and proliferated indefinitely as long as cellular contact was retained. Scanning and transmission electron microscopy confirmed intimate membrane-to-membrane contact between the adherent cells and parasites. Cellular contact, therefore, seemed to be essential for trypanosomal survival and growth. Immunocytochemical studies demonstrated intense fibroblast growth factor (FGF) activity in adherent cells, and FGFR-2 in associated trypanosomes. BioPorter Lucifer yellow protein delivery reagent studies demonstrated that Lucifer yellow transfected into fibroblast was incorporated into associated trypanosomes. The results suggest the existence of viable channels reminiscent of gap junctions between associated cells. Such transfer of low molecular weight molecules might represent antiapoptotic metabolic factors that support survival of adherent trypanosomes in vitro. Immunocytochemical studies also detected connexin-32 and connexin-43 in the cytoplasm of fibroblasts and associated trypanosomes, however, restriction of connexons to trypanosome/fibroblast adherent sites was not observed. Western blots confirmed the presence of connexin protein molecules in trypanosomes.

Fibronectin/fibroblast growth factor/cell matrix signaling pathways and reciprocal membrane interaction may be the regulators of cell growth and apoptosis in Trypanosoma musculi in co-cultures with fibroblasts.

Trypanosoma musculi cultivated in medium containing serum alone or in the absence of fibroblasts in vitro were transformed into rounded, immotile cells, incapable of division and infectivity. Only in close contact with fibroblasts could the parasites survive and grow indefinitely. This report established the identity of the splenic 'sustentacular' cells as fibroblasts and utilized immunocytochemistry to demonstrate the putative cytoskeletal and membrane-associated molecules that may be involved in the control of growth and division, and apoptosis of T. musculi in vitro. The results indicated that cells that reacted intensely for fibroblast growth factor (FGF) also displayed a complex cytoskeletal system of F-actin bands underlying the plasma membrane of the fibroblast cell body and its numerous processes. Among the cytoskeletal and membrane glycoproteins, fibronectin, I-CAM, laminin, occludin, vinculin and desmin were most prominent. Fibronectin was most highly enhanced on the cell membrane and deposited as 'finger prints or tracks' on the extracellular culture surfaces. Transmission and scanning electron microscopy confirmed the intimate contact between trypanosomes and fibroblasts, however, neither membrane fusion or junctions were apparent. Our results suggested that a fibroblast-derived, membrane-associated factor appeared to be the putative growth regulator and apoptosis inhibitor in co-cultures of spleen-derived fibroblasts and T. musculi.

Development and proliferation of Trypanosoma musculi in the presence of adherent splenic cells.

The development and proliferation of Trypanosoma musculi parasites were studied in vitro in the presence of adherent splenic cells. The parasites grew and proliferated only when attached by their flagellar tips to adherent splenic cells. Analyses of excretory-secretory products of the adherent cells-parasites did not indicate any detectable soluble growth factor that might be responsible for the growth of these trypanosomes. During the proliferation, the kinetoplast migrated toward the nucleus, and once in the vicinity of the nucleus, nuclear division was triggered. The nucleus and kinetoplast divided at the same time Trypanosoma musculi parasites started dividing from their flagellar ends, and daughter cells were formed within 48 hr. In the absence of adherent splenic cells in vitro, the parasites were transformed into round nonviable forms.