GASTROENTEROLOGY 1995;108:409-416 Human Eosinophils Migrate Across an Intestinal Epithelium in Response to Platelet-Activating Factor MURRAY B. RESNICK, SEAN P. COLGAN, CHARLES A. PARKOS, CHARLENE DELP-ARCHER, DEIDRE MCGUIRK, PETER F. WELLER, and JAMES L. MADARA Division of Gastrointestinal Pathology, Department of Pathology, and Departmentof Anesthesia, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts Background/Aims: Transmigration of eosinophils across intestinal epithelia occurs in a variety of muco- sal inflammatory disorders and results in the formation of crypt abscesses containing eosinophils. However, the conditions required to drive transepithelial migra- tion of eosinophils are not understood. Methods: This study investigated eosinophil migration across intesti- nal epithelia using purified eosinophils and confluent monolayers of the human intestinal epithelial cell line T84. Results: Unactivated eosinophils (i.e., no granulo- cyte/macrophage colony-stimulating factor [GM-CSF] preexposure) did not migrate across T84 monolayers in the presence of transepithelial gradients of C5a, n- formyl-methionyl-leucyl-phenylalanine (fMLP), or plate- let-activating factor (PAF). In contrast, activation of eosinophils by coincubation or pretreatment with GM- CSF enabled transepithelial migration in response to PAF but not to C5a or fMLP gradients in a time- and dose-dependent fashion. Specificity was confirmed by both the PAF receptor antagonist WEB-2086 and the PAF enantiomer 2-1yso-I~-acetyl-~-O-hexadecyi. Finally, addition of functionally inhibitory monoclonal antibod- ies to CD11b but not CD11a, very late activation anti- gen (VLA-4), or intraceltular adhesion molecule I inhib- ited eosinophil migration. Conclusions: These studies establish that physiologically directed migration of eo- sinophils across model epithelia occurs but that this process is governed by the state of eosinophil activa- tion, the specific chemotactic gradient imposed, and the availability of specific surface integrins to partici- pate in putative eosinophil-epithelial adhesion steps. I n diverse inflammatory states of a variety of organs lined by columnar epithelia, eosinophils migrate across epithelial barriers after their exit from the micro- vasculature. For example, eosinophil migration into the bronchial lumen plays a major role in the pathophysiol- ogy of allergic asthma. 1 Eosinophils also migrate into the intestinal lumen during a variety of disease states. In active eosinophilic proctocolitis, parasitic infections, and acute radiation enteritis, eosinophils are the major in- flammatory cells collecting in the intestinal crypt lumen, thus forming so-called eosinophilic crypt abscesses. 2-5 Additionally, eosinophilic infiltration into and across the intestinal epithelium is frequently observed in chronic idiopathic inflammatory bowel diseases such as Crohn's disease and ulcerative colitis. 6-8 In these disorders, ultra- structural studies have indicated that both the subepithe- lial and transmigrated eosinophils exist in an activated functional state. 6-8 In the geometrically confined micro- environment of the crypt abscess, several eosinophil prod- ucts including cationic proteins, oxygen metabolites, lipid mediators, and proteases may contribute to epithelial dysfunction. 1 Recently, we have shown that eosinophils, when exposed to conditions in the intestinal luminal microenvironment, elaborate 5'-adenosine mono- phosphate, a potent epithelial secretagogue 9 that is more potent on exposure to the apical than the basolateral membrane of epithelia. Similarly, other investigators us- ing tracheal epithelia have shown that exposure of the apical membrane to major basic protein, derived from eosinophil-specific granules, can stimulate ion transport processes such as electrogenic C1- secretion.l° Such obser- vations indicate that transepithelial migration of eosino- phils may uniquely influence epithelial function by allowing interaction of eosinophil products with the nor- mally sequestered apical membrane domain of columnar epithelia. Mobilization of eosinophils into inflammatory sites is dependent on the release of local chemoattractants and first involves eosinophil adhesion and transmigration through the endothelial wall. Whereas the complex adhe- sive interactions related to eosinophil transendothelial migration are being widely addressed, little is known of Abbreviations used in this paper: EPO, eosinophil peroxidase; fMLP, r~formyl-methionyl-leucyl-phenylalanine; GM-CSF,granulocyte/ macrophage colony-stimulating factor; HBSS, Hank's balancedsalt solution; ICAM, intercellularadhesionmolecule; 2-1yso-PAF, 2-1yso- J~-acetyl-7-O-hexadecyl; MAb,monoclonal antibody; PAF,platelet-acti- vating factor; PMN, polymorphonuclear neutrophilleukocyte; VLA-4, very late activationantigen. © 1995 by the American Gastroenterological Association 0016-5085/95/$3.00