Adhesion and Cytosolic Dye Transfer between Macrophages and Intestinal Epithelial Cells

Abstract

Activated macrophages (MQ) found in the intestinal lesions of patients with inflammatory bowel disease (IBD) secrete many inflammatory mediators which can regulate intestinal epithelial cell (IEC) function. However, little is known about direct MQ-IEC interactions. Two potential mechanisms by which cells may interact are through specific receptor-ligand binding of adhesion molecules, such as integrins or cadherins, and by exchange of cytoplasmic substances through transmembraneous channels called gap junctions. We investigated whether Mø could adhere to epithelial cells in culture and form transmembrane communication channels as defined by dye transfer. Primary cultures of murine Mø and a Mø cell line, P388D1, adhered to Mode-K and IEC6, but not CMT-93 IEC. Antibody blocking studies determined that P388D1-Mode-K binding was partially dependent on β2 integrin (CD18) function, Mode-K constitutively expressed CD106 (VCAM-1) and cell associated fibronectin, while P388D1 expressed low levels of CD49d/CD29 (VLA4) but blocking antibodies to these surface molecules did not inhibit P388D1-Mode-K adherence. Transfer of calcein dye from MQ to IEC was quantitated by flow cytometry and was dependent on Mø-IEC adhesion. Dye transfer was concentration dependent in that the fluorescence intensity of Mode-K was proportional to the number of adherent P388D1 cells as well as the dye load of the Mø. These results indicate that Mø interact with IEC by adhesion and possibly through gap junctions and may thus regulate IEC function by direct cell-cell communication.

Key Words:

• Macrophage
• Intestinal epithelial cells
• β2 integrin
• gap junction