Enterocyte expression of the eotaxin and interleukin-5 transgenes induces compartmentalized dysregulation of eosinophil trafficking

Eosinophils accumulate in the gastrointestinal tract in a number of medical disorders, but the mechanisms involved are largely unknown. To understand the significance of cytokine expression by enterocytes, enterocyte transgenic mice that overexpressed the eosinophil-selective cytokines eotaxin and interleukin (IL)-5 were generated. Transgenic mice, generated by utilizing the rat intestinal fatty acid-binding protein promoter (Fabpi), overexpressed the mRNA for these cytokines in the small intestine. Overexpression of IL-5 resulted in marked increases of eosinophils in the bone marrow and blood, whereas eotaxin overexpression resulted in similar levels compared with nontransgenic control mice. In contrast, both IL-5 and eotaxin transgenic mice had significant accumulation of eosinophils in the gastrointestinal mucosa compared with control mice. Eotaxin-induced gastrointestinal eosinophilia was substantially higher than that induced by IL-5 and was especially prominent within the lamina propria of the villi. Interestingly, genetic rescue of eotaxin deficiency (by transgenic overexpression of eotaxin in eotaxin gene-targeted mice) resulted in significant restoration of gastrointestinal eosinophil levels. Finally, the intestinal eosinophilia induced by the eotaxin transgene was β₇ integrin-dependent. Taken together, these results demonstrate that expression of eotaxin and IL-5 in intestinal epithelium induces compartmentalized dysregulation of eosinophil trafficking and the important role of the β₇ integrin in gastrointestinal allergic responses.