Evidence for another cell-adhesion molecule in Dictyostelium discoideum.

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Abstract
A rabbit antiserum that completely blocked cell-cell adhesion of aggregating D. discoideum cells was raised in an in vitro assay. All adhesion-blocking activity of this antiserum was absorbed with a D. discoideum fraction containing molecules having MW as high as .apprx. 106, even after the material had been extensively digested with Pronase. The antigenic determinants in this macromolecule are saccharide residues. Antigen-rich material is present on vegetative cells but accumulates on or around differentiating D. discoideum cells as they aggregate. The cell surface of an aggregating cell contains .apprx. 5 .times. 105 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.