Activated eosinophils evoke chloride secretion in model intestinal epithelia primarily via regulated release of 5′-AMP

Eosinophils may be prominent in intestinal diseases including allergic gastroenteritis, inflammatory bowel disease, enteritis associated with hypereosinophilic syndromes (HES), and parasitic diseases. Unlike normal blood eosinophils, those that circulate in HES and those that infiltrate inflamed tissue exhibit an "activated" phenotype. To model intestinal epithelial-eosinophil interactions, we used peripheral blood eosinophils and human crypt-like T84 epithelial cell-line monolayers. Eosinophils from normal, mildly atopic donors, only if activated by PMA or primed with granulocyte-macrophage-CSF for 48 h, as well as eosinophils from HES patients elicited a short circuit current when applied apically to T84 monolayers. This eosinophil-derived bioactivity, which was transferable in cell-free supernatants and in <1000 m.w. ultrafiltrates, stimulated electrogenic Cl^- secretion, as indicated by inhibition with basolateral bumetanide or gluconate substitution and by enhancement of the rate constant for ¹²⁵I efflux from preloaded T84 cells. This secretagogue activity was blocked in both intact activated eosinophils and in eosinophil-conditioned supernatants, by 8-phenyl-theophylline, indicating involvement of an adenosine receptor. Ion exchange and reversed-phase HPLC analyses demonstrated that eosinophil supernatant ultrafiltrates contained elevated levels of 5′-AMP that was converted to adenosine after incubation with epithelium. Inhibition of epithelial apical membrane ecto-5′-nucleotidase ablated the conversion to adenosine. These studies establish that activated eosinophils elicit Cl^- secretion from intestinal epithelia and that 5′-AMP released by eosinophils followed by its conversion to adenosine at the epithelial surface is the basis for this response.