NEUTROPHIL MIGRATION ACROSS CULTURED INTESTINAL EPITHELIAL MONOLAYERS IS MODULATED BY EPITHELIAL EXPOSURE TO IFN-GAMMA IN A HIGHLY POLARIZED FASHION

Neutrophil, or polymorphonuclear leukocyte (PMN), migration across intestinal epithelial barriers, such as occurs in many disease states, appears to result in modifications of epithelial barrier and ion transport functions (Nash, S., J. Stafford, and J. L. Madara. 1987. J. Clin. Invest. 80:1104-1113; Madara, J. L., C. A. Parkos, S. P. Colgan, R. J. MacLeod, S. Nash, J. B. Matthews, C. Delp, and W. I. Lencer. 1992. J. Clin. Invest. 89:1938-1944). Here we investigate the effects of epithelial exposure to IFN-gamma on PMN migration across cultured monolayers of the human intestinal epithelial cell line T84. Transepithelial migration of PMN was initially assessed in the apical-to-basolateral direction, since previous studies indicate general qualitative similarities between PMN migration in the apical-to-basolateral and in the basolateral-to-apical directions. In the apical-to-basolateral direction, epithelial exposure to IFN-gamma markedly upregulated transepithelial migration of PMN in a dose- and time-dependent fashion as measured by both electrical and myeloperoxidase assays. This IFN-gamma-elicited effect on transmigration was specifically due to a. IFN-gamma effect on epithelial cells and was not secondary to IFN-gamma effects on epithelial tight junction permeability. Moreover, this IFN-gamma effect was dependent on epithelial protein synthesis, and involved a pathway in which CD11b/18, but not ICAM-1 or CDlla/18, appeared to play a crucial role in PMN-epithelial adhesion. IFN-gamma also substantially modified PMN transepithelial migration in the natural, basolateral-to-apical direction. The IFN-gamma effect on naturally directed transmigration was also specifically due to an IFN-gamma effect on epithelial cells, showed comparable time and dose dependency to that of oppositely directed migration, was CD11b/18 dependent, and required epithelial protein synthesis. Additionally, however, important qualitative differences existed in how IFN-gamma affected transmigration in the two directions. In contrast to apical-to-basolateral directed migration, IFN-gamma markedly downregulated transepithelial migration of PMN in the natural direction. This downregulation of PMN migration in the natural direction, however, was not due to failure of PMN to move across filters and into monolayers. Indeed, IFN-gamma exposure to epithelia increased the number of PMN which had moved into the basolateral space of the epithelium in naturally directed transmigration. These results represent the first detailed report of influences on PMN transepithelial migration by a cytokine, define conditions under which a qualitative difference in PMN transepithelial migration exists, and suggest that migration of PMN across epithelia in the natural direction may involve multiple steps which can be differentially regulated by cytokines. Specifically, it appears that in naturally directed migration, IFN-gamma may enhance the retention time of the recruited PMN in the paracellular space below tight junctions, and does so, at least in part, by downregulating a PMN-epithelial interactive event required for subsequent transjunctional migration. We speculate that such retention of PMN at this specific anatomic location, the site wherein the transition from the external environment to the internal milieu occurs, may serve an important role in mucosal defense.