Immune roles of a rhamnose-binding lectin in the compound ascidian Botryllus schlosseri.

The present communication describes the immune role played by a recently identified member of the rhamnose-binding lectin (RBL) family from the colonial ascidian Botryllus schlosseri. B. schlosseri RBL (BsRBL) can activate phagocytes through: i) induction of their directional movement towards the source of the molecule; ii) modification of cytoskeleton, required for shape changes; iii) stimulation of the respiratory burst, and consequent production of reactive oxygen species (ROS) with microbicidal activity, including superoxide anions and peroxides; and iv) increase in the ability to phagocytose foreign particles. RBL also induces the synthesis and release, by cytotoxic morula cells (MCs), of cytokines recognized by anti-IL1α and anti-TNFα antibodies. At high concentrations, BsRBL induces degranulation of MCs and the consequent release of the cytotoxic enzyme phenoloxidase into the medium. Results are consistent with the existence of cross-talk between B. schlosseri immunocytes (phagocytes and MCs). In addition, a three dimensional model for BsRBL is presented.