Theophylline blocks the effect of dilazep on APS IgG-induced monocyte TF activity. Normal monocytes were stimulated with APS IgG (250 μg/mL), LPS (500 ng/mL), or unstimulated (control) in the presence of dilazep (100 μg/mL), theophylline (100 μg/mL), or both dilazep and theophylline. Cells were then washed and assayed for TF activity. Data shown are the mean ± SEM of duplicate determinations. Assays of APS IgG were performed in the presence of β2GPI (100 μg/mL).