Intestinal NF-κB is activated, mainly as p50 homodimers, by platelet-activating factor

NF-κB, a transcription factor, upregulates gene transcription of many inflammatory mediators. Here, we examined the activity of NF-κB in the rat small intestine, and how it may be affected by platelet-activating factor (PAF), an important mediator for intestinal injury and inflammation. Ileal nuclear extracts from sham-operated and PAF (1.5 μg/kg)-injected rats were prepared for the assessment of NF-κB DNA-binding activity, and the identification of NF-κB subunits. The experiment was also performed on neutrophil-depleted rats to examine whether the PAF effect is neutrophil-dependent. Cellular NF-κB was localized by immunohistochemistry. We found that: (a) NF-κB is constitutively active in rat small intestine; (b) PAF at a dose below that causing shock and bowel necrosis enhances DNA-binding activity of NF-κB within 30 min after injection; activated NF-κB contains predominantly p50 subunits; (c) immunohistochemistry showed that PAF induced translocation of p50 into the nucleus of cells of the lamina propria, as well as of the epithelium; and (d) the effect of PAF is abrogated by neutrophil depletion, suggesting a role of neutrophils in NF-κB activation. Our study suggests that NF-κB is weakly active constitutively in the intestine, and inflammatory stimuli such as PAF activate NF-κB and enhance its DNA-binding activity in the intestine, which contains predominantly p50 subunits.