(iv) Synthetic peptides representing region I from the P.falciparum CS protein and region II-plus from the P.falciparum, P.berghei or P.vivax CS protein inhibit in vitro translation. We propose that Plasmodium manipulates hepatocyte protein synthesis to meet the requirements of a rapidly developing schizont. Since macrophages appear to be particularly sensitive to the presence of CS protein in the cytosol, inhibition of translation may represent a novel immune evasion mechanism of Plasmodium. Keywords: circumsporozoite protein/immune evasion/ membrane translocation/Plasmodium/protein synthesis IntroductionAfter the discovery that circumsporozoite (CS) protein is the most abundant protein on the surface of malaria sporozoites in the early 1980s (reviewed in Nussenzweig and Nussenzweig, 1985), the function of CS protein remained unknown for many years. Recent evidence suggests that the CS protein is a multifunctional molecule that plays a crucial role at various points of the malaria life cycle. CS protein is translocated continuously from the anterior to the posterior cell pole and has, therefore, been implicated in sporozoite gliding motility (Stewart and Vanderberg, 1991). The finding that malaria sporozoites invade the liver of the vertebrate host within minutes after 3816 © Oxford University Press transmission by an infected mosquito (Shin et al., 1982) suggested a receptor-mediated clearance mechanism. We and others have shown that the CS protein binds to highly sulfated, heparin-like oligosaccharides in heparan sulfate on the basolateral membrane of hepatocytes in the space of Disse (Cerami et al., 1992;Pancake et al., 1992;Frevert et al., 1993;Ying et al., 1997), and this interaction is held responsible for the rapid and selective targeting of the sporozoites to the liver sinusoid Sinnis et al., 1994Sinnis et al., , 1996. In vitro, the CS protein binds with high affinity to the low density lipoprotein receptorrelated protein (LRP), and the dual interaction with heparan sulfate and LRP plays a dominant role in sporozoite invasion (Shakibaei and Frevert, 1996). Most recently, CS protein knock-out studies have demonstrated the crucial involvement of the CS protein in the formation of sporozoites in the mosquito midgut (Ménard et al., 1997), and the presence of receptors on salivary glands has suggested a role for the CS protein in sporozoite adhesion to this organ of the mosquito (Sidjanski et al., 1997).We present data here which show that the CS protein may also have a function within cells of the vertebrate host. Upon cell contact, Plasmodium berghei and P.yoelii sporozoites actively translocate CS protein across the cell membrane into the cytoplasm of mammalian cells in vitro (Hügel et al., 1996). This translocation occurs in the absence of parasite invasion by an as yet unknown mechanism. It requires neither the metabolic nor the endocytic machinery of the mammalian cell. The CS protein spreads throughout the entire cytosol of the affected cell and binds to cytosolic and endoplasmic reticulumassociated r...

No abstract

Theileria annulata-infected bovine cells as well as mitogen-stimulated bovine peripheral blood mononuclear cells (PBMC) express a proliferation-associated nuclear protein equivalent to the human Ki-67 protein. In analogy to the human system, the expression of the bovine Ki-67 protein is restricted to proliferating cells only, since (a) Ki-67 expression paralleled [3H]-thymidine incorporation in concanavalin A (Con A)-stimulated bovine PBMC, (b) Ki-67 was not detectable in quiescent bovine cells, and (c) Ki-67 expression in Theileria-infected cells is related to the presence of the parasites within the cytoplasm of the host cells; upon treatment with the theilericidal drug buparvaquone the parasites are destroyed and the cells cease to proliferate and to express the Ki-67 protein. Western-blot analysis of lysates of proliferating bovine cells revealed that the prototype monoclonal antibody Ki-67 and the new equivalent antibody MIB-1 detected one prominent protein band with an apparent molecular weight of 430 kDa. Two cDNA clones (pUC18.B1.Ki-67 and pUC18.B2.Ki-67) were isolated from a lambdagt11 cDNA library of T. annulata-infected bovine cells by immunoscreening with the monoclonal antibody MIB-1. Comparison of these cDNA sequences with those of the human Ki-67 protein revealed 60-70% identity. Within the "Ki-67 motif", identity proved to be 80% at the amino acid level. The remarkable identity between bovine and human Ki-67 proteins suggests that MIB-1 can be used as a marker for cell proliferation in animal research. In this context we could identify proliferating cells in lymph nodes of Theileria-infected animals and, furthermore, we could distinguish between infected and uninfected proliferating cells using MIB-1 and an antiserum against a recombinant parasite protein designated SA288.

T. annulata-infected cells present infection-associated peptides. These peptides represent target molecules of the cytotoxic acting cells. Their preparation and characterization may help to develop a sub-unit vaccine. Our studies show that macroschizont-infected bovine cells can be used as parasite antigen in serology for the detection of parasite-specific antibodies in serum of infected animals. Primers derived from the macroschizont of T. annulata can be used as molecular tools for the detection of parasite DNA in blood samples of carrier cattle.