Enhancement of monocyte TF activity by APS IgG is not due to contamination with endotoxin (LPS). (A) Polymyxin B (100 U/mL) inhibits monocyte TF activity induced by LPS (500 ng/mL) but not by an APS patient IgG (500 μg/mL). (B) Heating to 100° C for 10 minutes destroys the ability of APS IgG to stimulate monocyte TF activity but has no effect on LPS. Assays of APS IgG were performed in the presence of β2GPI (100 μg/mL). Data shown are the mean ± SEM of duplicate determinations.