A large body of evidence suggests that oxidized LDL (oxLDL) has a role in atherogenesis. One effect is the impact on macrophage function. We have studied the effects of oxLDL and oxysterols on the binding of the transcription factors nuclear factor (NF)-kappaB and AP-1 to DNA. These transcription factors are involved in the regulation of several genes and expressed during activation of macrophages, for example by endotoxin (LPS). OxLDL did not induce binding of NF-kappaB. However, the LPS-induced response to NF-kappaB was substantially reduced after preincubation with oxLDL. Medium and highly oxidized LDL also decreased the constitutive DNA-binding of AP-1. Similar effects on AP-1-binding were seen with the oxysterols, 7beta-hydroxycholesterol, 24- hydroxy-, 25-hydroxy-, and 27-hydroxy-cholesterol. Our data therefore suggest an effect of oxLDL on the DNA-binding of AP-1, which might be mediated by the oxysterol content of oxLDL. A decreased LPS-induced TNF-alpha and IL-1beta mRNA and protein expression were found in macrophages incubated with oxLDL before LPS-exposure. These observations suggest that macrophages that internalize extensively oxidized LDL are suppressed in their response to inflammatory stimulation.