Identification and preliminary characterization of a Ca2+-dependent hemagglutinin in the coelomic fluid of Sipunculus nudus.

A soluble agglutinin was purified by affinity chromatography of the celomic fluid of the marine worm Sipunculus nudus. This agglutinin requires metal cations for its activity and is specific for derivatives of D-galactose. It resulted lightly thermostable, with a pH optimum around 7.5. On SDS-PAGE, it was resolved in two bands, of 33 and 31 kDa in reducing conditions and 29 and 26 kDa in non-reducing conditions. This behavior is probably due to the presence of disulfide bridges between cysteine residues, which are required for the correct functioning of the hemagglutinin, as β-mercaptoethanol completely abolish the agglutinating activity of cell-free celomic fluid. The purified lectin can influence in vitro phagocytosis of yeast by celomic leukocytes: in the presence of the molecule, ingestion of foreign particles results significantly decreased and yeast cells agglutinate and forms rosettes around the celomocytes. This suggests a role of the molecule in immunosurveillance.