Inhibition of intercellular adhesion in a cellular slime mould by univalent antibody against a cell-surface lectin

Abstract

THE cellular slime moulds, Dictyostelium discoideum and Polysphondylium pallidum contain carbohydrate-binding proteins (lectins) that increase significantly in amount in soluble crude extracts as amoebae differentiate from the vegetative stage (when the cells do not associate) to the aggregation-competent stage (when the cells can form stable intercellular contacts)^1–3. Lectins from the two species, assayed as agglutinins of erythrocytes, have been purified by affinity techniques and, on the basis of their carbohydrate-binding specificities, as well as several physicochemical properties, have been shown to be distinct proteins^3–5. Distinct lectin activities have also been identified in four other species of slime moulds⁶. The lectins from D. discoideum and P. pallidum accumulate on the cell surface with development of aggregation competence as demonstrated by erythrocyte–rosette experiments^1,2,7, immunofluorescent and immunoferritin techniques^7,8, and lactoperoxidase-catalysed iodination of intact cells⁹. Both species also contain cell-surface receptors with a very high affinity for the homotypic lectin and a lesser affinity for the heterotypic lectin¹⁰, suggesting a possible basis for species-specific intercellular affinities. In the case of D. discoideum, we have shown that the high affinity receptor appears on the cell surface as amoebae differentiate into the cohesive state¹⁰.