Konkurrenz und Umweltschutz. Wald- und Holzwirtschaft zwischen Ökonomie und Ökologie

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Proteolytic cleavage of surface proteins enhances susceptibility of lymphocytes to invasion by Theileria parva sporozoites

A flow cytometric method using anti-parasite antibodies was developed to measure binding of theileria parva sporozoites to the target bovine lymphocyte membrane. Parasite-host cell interactions could be inhibited by monoclonal antibodies to bovine MHC class I and partially by one of two antibodies to BoCD45R. Proteolysis of the lymphocyte surface removed CD45R but not MHC class I determinants, and enhanced sporozoite binding. These observations support the hypothesis that CD45R and CD45R antibodies may non-specifically prevent close approximation between sporozoites and lymphocytes. Interestingly, under normal conditions, sporozoites of T. parva did not attach to lymphocytes from goats, but did so when the cells were treated with the protease, suggesting that receptor(s) for T. parva sporozoites might be present on caprine cells but are not easily accessible. These and other results indicate that proteases may be involved in binding and entry of T. parva sporozoites. Electron microscopy revealed that the process of binding and entry of sporozoites into protease-treated goat lymphocytes was very similar to that of the bovine cells. However, schizonts did not develop and lymphocyte proliferation was not induced, indicating that cell entry by sporozoites and cellular transformation are separate processes

Theileria parva isolate of low virulence infects a subpopulation of lymphocytes

Theileria parva is a tick-transmitted protozoan parasite that infects and transforms bovine lymphocytes. We have previously shown that Theileria parvaChitongo (TpC) is an isolate of lower virulence than T.parvaMuguga (TpM). Lower virulence appeared correlated with a delayed onset of thelogarithmic growth phase of TpC-tranformedperipheral blood mononuclear cells after in vitro infection. In the current study, infection experiments of WC1(+)-gammadelta-T cellsrevealed thatonly TpMcould infect these cells andthat no transformed cells could be obtained withTpC sporozoites. Subsequent analysis of susceptibility of different cell lines and purified populations of lymphocytes for infection and transformation by both isolates showed that TpMsporozoites could attach and infectCD4(+), CD8(+) and WC1(+) T lymphocytes, but that TpCsporozoites were only observed to bind to the CD8(+) T cell population. Flow cytometry analysis of established,transformed clones confirmed this bias in target cells. TpM-transformed clones consisted of different cell surface phenotypes, suggesting that they were derived from either host CD4(+), CD8(+)or WC1(+)T cells. In contrast, all in vitro and in vivoTpC-transformed clones expressed CD8 but not CD4 or WC1, suggesting that the TpC-transformed target cells were exclusivelyinfected CD8(+) lymphocytes.So a role of cell tropism in virulence is likely. Since the adhesion molecule p67 is 100 % identical between the two strains, a second, high affinity adhesin that determines target cell specificity appears to exist

Characterization of cysteine proteases from the carcinogenic liver fluke, Opisthorchis viverrini

Protease activities in extracts of Opisthorchis viverrini were investigated using gelatin zymography and fluorogenic peptide substrates. Using gelatin-impregnated X-ray film, 2 microg of O. viverrini excretory-secretory products (Ov-ES) and adult somatic extract (Ov-SE) showed proteolytic activity. Zymography of both O. viverrini extracts revealed bands at approximately 30 kDa. Using fluorogenic peptide substrates, the majority of O. viverrini activity was determined to be cathepsin L-like cysteine protease (cleaved Z-Phe-Arg-aminomethylcoumarin (AMC)) whereas little or no activity was ascribable to other classes of proteases. The O. viverrini cysteine protease activity was greatest at pH 6.0 and the activity was inhibited by the class-specific inhibitors, E-64 and Z-Ala-CHN2. Chromatographic purification of O. viverrini cysteine proteases on thiol-sepharose enriched for protein(s) of approximately 30 kDa from Ov-ES and Ov-SE. The activity profile of the purified enzyme was similar to that of the cathepsin L-like activity characterized in Ov-SE and Ov-ES. Furthermore, determination of cysteine protease activity in several developmental stages of the parasite revealed the highest protease activity in metacercariae soluble extract, followed by Ov-ES, egg soluble extract, and Ov-SE. These findings demonstrated that O. viverrini has a cathepsin L-like cysteine protease(s) and suggested that abundant cysteine protease activity was present in metacercariae where the hydrolase might be involved in cyst excystation during mammalian infection