 Seemingly, CYP1A1 activity in the intestinal mucosa prevents major amounts of ingested benzo["a"]pyrene to enter portal blood and systemic circulation.Intestinal, but not hepatic, expression of CYP1A1 depends on TOLL-like receptor 2 (TLR2), which is a eukaryotic receptor for bacterial surface structures such as lipoteichoic acid.Moreover, B"a"P has been found to activate a transposon, LINE1, in humans.