Inhibition of NB-4 cell aggregation by MoAb and 10 mmol/L EDTA. NB-4 cells were exposed to 100 nmol/L tRA for 72 hours. Homotypic aggregation was measured as described in Materials and Methods. Blocking concentrations of the indicated MoAbs were added at the initiation of the assay, and the percent aggregation ± SD was determined at 6 hours. Data represent results from three separate experiments performed in duplicate.