In Vivo Effects of A Pro-PO System Inhibitor on the Phagocytosis of in Larvae.

is a Gram-negative bacterium symbiont of the entomopathogen nematode whose immunosuppressive properties over host's immune response have been thoroughly investigated. In particular, live actively impairs phagocytosis in host's hemocytes through the secretion of inhibitors of eicosanoids synthesis. In this article we have investigated the cell surface structural features of responsible for the elusion from phagocytosis. To this end we have studied the uptake of heat-killed (hk), fluorescein isothiocyanate (FITC)-labeled by phagocytes from both a host insect and a mammalian species. In vitro dead passively resists engulfment by insect hemocytes without impairing the phagocytosis machinery whereas, unexpectedly, in vivo a significant phagocytosis of dead was observed. in vivo phagocytosis was increased by the co-injection of the specific inhibitor of pro-phenoloxidase (PO) system phenylthiourea (PTU), even if these effects were not observed in in vitro tests. Furthermore, biochemical modifications of cell wall implement in vivo phagocytosis, suggesting that this bacterium avoid phagocytosis because the ligand of phagocytic receptors is somehow buried or disguised in the cell wall. Finally, dead escapes engulfment even by human phagocytes suggesting that could be a useful model to investigate escape from phagocytosis by mammalian macrophages.