CD9 ligation promotes adhesion of EML-C1 cells to many stromal cells that express a CD9-associated 100 kD molecule. The adherent cells used in this panel were surface-labeled and analyzed by immunoprecipitation as illustrated in Fig 6 and, with the exception of NIH3T3 fibroblasts, all had a 100 kD protein that associated with CD9. EML-C1 cells were plated on each of these adherent cell types in the presence of 1 μg/mL KMC8.8 or isotype-matched control antibodies before evaluation of adhesion as described in the Materials and Methods. Results represent the mean ± SD of triplicate cultures. Statistically significant differences from control values are indicated by two (P < .01) asterisks.