T-cell mediated acute inflammation of the ileum may occur during Crohn’s disease exacerbations. During ileal inflammation absorption of nutrients and electrolytes by villous cells is decreased with a concomitant increase in crypt and or villus fluid secretion. These alterations lead to fluid accumulation and the subsequent diarrhea. Net intestinal fluid secretion consists of HCO₃^- rich plasma-like fluid. However, the regulation and mechanisms of HCO₃^- secretion in normal and acutely inflamed ileum are not clearly understood. To study this phenomenon, anti-CD3 mAb induced in vivo ileal inflammatory mice models were used for in vitro functional studies with Ussing chamber and pH stat techniques. Three hours after anti-CD3 mAb injection, ileal mucosa stripped of muscular and serosal layers showed a significant increase in Isc (0.58 ± 0.07µEq/h.cm² vs 1.63 ± 0.14 µEq/h.cm²). The cAMP-stimulated Isc component was sensitive to glibenclamide but not to DIDS, suggesting that a CFTR mediated anion conductance was responsible. Basal Cl-dependent HCO₃^- secretion, measured using pH stat technique, was decreased significantly in anti-CD3 injected mice, with a simultaneous increase in Cl^-independent HCO₃^- secretion that was also inhibited by glibenclamide. Experiments using CFTR-/- mice showed neither an increase in Isc nor an increase in HCO₃^- secretion, confirming the role for CFTR protein in stimulating anion secretion following anti-CD3 treatment. Western blot analysis indicated that CFTR protein levels were unaltered by anti-CD3 treatment, at least acutely. Finally, an immunoassay for cAMP showed significant increases in intracellular cAMP in villus cells, but not in crypt cells. These studies therefore suggest a shift from a predominantly electroneutral Cl^--HCO₃^- exchange in normal mice to a predominantly electrogenic anion secretion including HCO₃^- that occurs via functional CFTR during anti-CD3 mediated acute inflammation.