A new method is presented for the quantitative analysis of intercellular adhesive specificity. In this assay, two cell types are mixed, one unlabeled and the other labeled with the fluorescent dye, fluorescamine [4-phenylspiro(feran-2[3H],1'-phthalan)-3,3'-dione]. The resulting aggregates are analyzed by fluorescence microscopy to determine the number of labeled and unlabeled cells per aggregate. Random (nonspecific) aggregation was characterized by a binomial distribution, and adhesive specificity was accordingly quantified by the deviation (as determined by a chi-square test) from the calculated binomial distribution. The labeling procedure was simple and rapid, and experiments with 18 different cell types showed that it did not affect cell viability, morphology, rate and extent of adhesion, plating efficiency, and the capability of myogenic cells to undergo terminal differentiation. Most important, assays with morphologically identifiable cell pairs indicated that the fluorescent label neither induced apparent nor destroyed existing adhesive specificity. The most pronounced adhesive specificities were observed with freshly explanted cells from adult tissues and also with mixtures of simian virus 40-transformed and nontransformed BALB/c 3T3 cells. A glucosamine-6-phosphate N-acetylase-deficient mutant 3T3 line (AD6), however, aggregated randomly with parental 3T3 cells. Lectin-resistant mutant Chinese hamster ovary (CHO) cells displayed marginal adhesive specificity when mixed with normal CHO cells.

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