Homotypic cell aggregation (cell–cell adhesion)assay
A homotypic aggregation assay was performed as reported previously (Cho et al., 2001). Briefly, U937 cells were pre-incubated with each fraction (100 g/ml) at 37◦C for 1h and further incubated with aggregative antibodies (1 g/ml) in 96-well plate. After 6-h incubation, the cultures were examined with an inverted light microscope equipped with a COHU high performance CCD (Diavert) video camera. Four random fields of each well were captured and analyzed using NIH image software in order to calculate the average size of the clusters.