A modification of an assay for intercellular adhesive specificity is described. The method involves the collection of radioactively labeled cells by aggregates of the same (isotypic aggregates) or different (heterotypic aggregates) types of tissue and determination of the number of cells collected by liquid scintillation counting. The use of 32P to label the tissues permitted a much more rapid estimation of cell collection than was obtained previously. With the use of chick embryo neural retina, liver, forebrain, pectoral muscle, and heart ventricle tissue, it was shown that isotypic was always greater than heterotypic collection. Labeled neural retina cell collection by neural retina aggregates was studied as a function of time, cell suspension density, aggregate diameter, temperature, and aggregate number. Neural retina aggregates were treated with certain enzymes in an attempt to determine whether specific changes on the surface of the aggregates would interfere with labeled neural retina cell collection. Of the various proteases and glycosidases tested, only ß-galactosidase rendered the surface more nonspecific.

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