The CrBV glycoprotein CrV1 and its homologue CcV1 from CcBV have also been implicated in altering haemocyte function. Asgari et al. (1997) showed that injection of a recombinant CrV1 protein into host P. rapae caterpillars caused haemo-cyte changes which were indistinguishable from those observed after PDV infection. CrV1 was in particular reported to alter actin distribution in haemocytes. Purified recombinant CrV1 was also shown to be endocytosed by host haemocytes after in vitro incubation (Asgari and Schmidt, 2002), suggesting that the protein may act intra-cellularly. Recently a yeast two-hybrid screen and co-immunoprecipitation experiments revealed that the CrV1 homologue, CcV1, interacts with hemolin (Labropoulou et al., 2008). Hemolin is a member of the immunoglobulin superfamily and is considered in insects to play the role of a pattern-recognition molecule capable of binding lipopolysaccharide of Gram-negative bacteria. The interaction between CcV1 and hemolin was shown to interfere with the capacity of hemolin to bind to lipopolysaccharide and induce bacterial agglutination. Furthermore Bombyx mori haemocytes, T. ni High Five, Drosophila melanogaster S2, and S. lit-toralis Sl2b lines all showed dramatic decrease in their ability to phagocytose E. coli in the presence of purified CcV1 protein. CcV1 was also shown to be taken up by High Five cells and B. mori haemo-cytes; however; protein co-localization experiments showed that CcV1 and hemolin interact at the cell surface. Therefore, these PDV glycoproteins may affect haemocyte phagocytosis at the level of the cell surface through interaction with hemolin and at an intracellular level, by a mechanism which is not yet characterized.
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