Inhibition of 185-4 cell growth induced by aggregated IgG. (A) The 185-4 cells were cultured with aggregated IgG (50 μg/mL) in the presence of medium alone, 10 μg of anti-FcγRII/III MoAb (2.4G2), 10 μg/mL of rat IgG as a control of 2.4G2, EGTA (1 mmol/L), FK506 (100 nmol/L), or staurosporine (10 μmol/L) for 24 hours, then viability was examined by the MTT assay. The results are means ± SD of the OD570 of triplicate cultures. Cultures with medium alone or with rIL-3 (50 U/mL) were the negative and positive controls of cell viability, respectively. (B) Inhibition of IL-3 production from 185-4 cells by aggregated IgG. The 185-4 cells were cultured with aggregated IgG in the presence of blocking reagents for 3 hours. Culture supernatants were harvested and dialyzed for the IL-3 assay as described in the legend to Fig 1. Data represent mean ± SD of five replicates.