Identification of a Human Enterocyte Lipoxin A₄ Receptor That Is Regulated by Interleukin (IL)-13 and Interferon γ and Inhibits Tumor Necrosis Factor α–induced IL-8 Release

Epithelial cells of the alimentary tract play a central role in mucosal immunophysiology. Pathogens and/or agonists that interact with mucosal surfaces often elicit epithelial responses that upregulate inflammation. Therefore, it was of interest to explore potential epithelial targeted antiinflammatory signals. Here we identified and sequenced a human enterocyte lipoxin (LX) A₄ [5(S),6(R),15(S)-trihydroxy-7,9,13-trans-11-cis eicosatetraenoic acid] receptor, and demonstrate that transcription of this receptor was controlled by cytokines, of which lymphocyte-derived interleukin (IL)-13 and interferon γ were the most potent. When lipoxins and LXA₄ stable analogs were evaluated for enterocyte functional as well as immune responses, lipoxins sharply inhibited TNF-α–induced IL-8 release but did not alter either barrier function or agonist-stimulated chloride secretion. 15R/S-methyl-LXA₄ and 16-phenoxy-LXA₄ each attenuated (IC₅₀ ∼10 nM) IL-8 release. Cyclooxygenase (COX) II is emerging as an important component in wound healing and proliferation in intestinal epithelia and when acetylated by acetylsalicylic acid (aspirin) initiates the biosynthesis of a LXA₄ receptor ligand. We therefore determined whether colonic cell lines (HT-29 Cl.19A, Caco-2, or T84) express the COX II isozyme. Results for RT-PCR and Western blot analysis showed that COX I as well as an IL-1β– and TNF-α–inducible COX II are expressed in HT-29 Cl.19A. In addition, aspirin-treated enterocytes generated 15R-HETE, a precursor of 15-epi-LXA₄ biosynthesis, whose potent bioactions were mimicked by the stable analog 15R/S-methyl-LXA₄. Taken together, these results identify an endogenous pathway for downregulating mucosal inflammatory events and suggest a potential therapeutic benefit for LXA₄ stable analogs.