Evidence for another cell-adhesion molecule in Dictyostelium discoideum.

We raised a rabbit antiserum that completely blocked cell-cell adhesion of aggregating Dictyostelium discoideum cells in an in vitro assay. All adhesion-blocking activity of this antiserum was adsorbed with a D. discoideum fraction containing molecules having molecular weights as high as about 10(6), even after the material had been extensively digested with Pronase. The properties of this fraction indicate that the antigenic determinants in this macromolecule are saccharide residues. Antigen-rich material is found on vegetative cells but accumulates on or around differentiating D. discoideum cells as they aggregate. The cell surface of an aggregating cell contains about 5 X 10(5) antigenic sites. Antigen is also abundant in the medium of D. discoideum cells starved in suspension, which proved the most convenient starting material for its purification. Like several other macromolecules already discovered in D. discoideum by using this immunological approach, the material identified here may play a direct or indirect role in cell-cell adhesion and merits tentative consideration as a cell-adhesion molecule.