Purified IgG from some APS patient sera increases TF activity on normal monocytes. Monocytes from healthy individuals were incubated with IgG (250 μg/mL) from 16 patients with APS (▨), IgG from a healthy individual (Nl, ▩), LPS (500 ng/mL, ▪), or media alone (M, □) in the presence of β2GPI (100 μg/mL). After 6 hours, cells were washed and assayed for TF activity as described. Results are expressed as the mean ± SEM of duplicate determinations.