Inducible lectins with galectin properties and human IL1 alpha epitopes opsonize yeast during the inflammatory response of the ascidian Ciona intestinalis

Hemocytes from the ascidian Ciona intestinalis exert in vitro Ca2+-dependent cytotoxic activitytoward mammalian erythrocytes and K562 cells. To examine the lytic mechanism, hemocytepopulations were separated (B1-B6 bands) through a Percoll discontinuous density gradient, thehemocyte cytotoxic activity (HCA) and the lytic activity of the hemocyte lysate supernatant (HLS)were assayed. In addition the separated hemocytes were cultured and the cell free medium (CFM)assayed after 3h culture. Results support that unilocular refractile hemocytes (URGs), enriched inB5, are cytotoxic. The B5-HLS contains lysins and the activity of B5-CFM shows that lysisns canbe released into a culture medium. The B5 activity was blocked by D-Galactose, α-Lactose,Lactulose, LacNAc, thiodigalactoside (TDG), L-Fucose, D-Mannose, D-Glucose, sphingomyelin(SM), and soluble phospholipase A2 (sPLA2) inhibitors (dibucain, quinacrine). Accordingly, HLSchemico-physical properties (alkaline medium, high termostability, Ca2+-dependence, trypsintreatment, protease inhibitors) and SEM observations of the affected targets suggested that sPLA2could be responsible for changes and large alterations of the target cell membrane. An apoptoticactivity, as recorded by a caspase 3, 7 assay, was found by treating K562 cells with very dilutedHLS. A lytic mechanism involving sPLA2 and lectins promptly released by URGs and morula cellsrespectively is suggested, whereas target cell membrane SM could be a modulator of the enzymeactivity.