Anti-β₂GPI peptide Abs activate TLR4. (A) HEK293T4 cells were treated for 24 hours with E coli LPS 1 ng/mL (bar 1), 100 pg/mL (bar 2), and 10 pg/mL (bar 3); endotoxin-free human anti-β₂GPI peptide Abs 100 μg/mL (bar 4), 50 μg/mL (bar 5), and 10 μg/mL (bar 6); endotoxin-free human anti-BSA Abs 100 μg/mL (bar 7), 50 μg/mL (bar 8), and 10 μg/mL (bar 9); serum deprived of anti-β₂GPI peptide Abs 100 μg/mL (bar 10); and untreated cells (bar 11). Results are expressed as a percentage of positive control, where the positive control is the mean OD value obtained on stimulation of HEK293T4 cells with 1 ng/mL of E coli LPS. Values are the means ± SDs of 3 different experiments. (B) Inhibition of HEK293T4 cell activation (NF-κB) induced by human anti-β₂GPI peptide Abs using β₂GPI peptide or an unrelated peptide. The y-axis represents the percentage of inhibition, and the x-axis indicates inhibitor concentrations.