Putative rhamnose-binding lectin in the solitary ascidian Ciona intestinalis.

Lectins are sugar-binding proteins involved in cell-cell interaction and the recognition of carbohydrate-containing molecules. They act as humoral factors in non-self recognition, are a key component of the innate immune systems of many metazoans and are involved in phagocyte activation through their opsonizing activity. In recent years, a new lectin family, the rhamnose-binding lectin (RBL) family, has been described and its members can modulate the inflammatory response in fish (Watanabe et al., 2009) as well as in various invertebrates, including the colonial tunicate Botryllus schlosseri. Recently, we succeeded in purifying, by affinity chromatography using a rhamnose column, a putative RBL, from the hemolymph of the solitary ascidian Ciona intestinalis. The molecule is Ca2+-independent and promptly (within 4h) inducible, after LPS inoculation. The eluted fractions, when examined by 15 % SDS-PAGE under reducing condition, showed four bands with apparent molecular masses of 65, 54, 30 and 19 kDa. The agglutinating activity of the isolated fraction was demonstrated using trypsinized rabbit erythrocytes and it was inhibited by glycosides such as rhamnose, galactose and lactose. Moreover, by immunocytochemical analysis using antibodies produced against B. schlosseri RBL and in situ hybridization with a riboprobe for the annotated C. intestinalis RBL, we have observed a positive signal in hyaline and granular amoebocytes and in the endothelium of the pharynx vessels.