Hollow-fiber assay for ligand-mediated cell adhesion.

Abstract

The investigation of receptor-ligand interactions in the cellular context presents significant technical challenges, first, to immobilize the ligand in a manner that preserves functional properties and, second, to relate ligand properties to cell adhesion and other cellular processes. Ligand-mediated cell adhesion was characterized by the development of a cellulose hollow-fiber adhesion assay in which ligand (protein A) was immobilized onto the cellulose membrane as a recombinant fusion protein containing a cellulose-binding domain affinity tag. Modules containing single cellulose hollow fibers were connected to a micro-flow system for cell deposition and detachment with fluid shear stress. The cell adhesion process that occurred inside a segment of hollow fiber was observed in real time by using an inverted microscope equipped with a CCD camera and digital frame grabber. Image analysis software was developed to count cells and record digital images. Cell adhesion strength was characterized by counting the number of cells that were detached by application of fluid shear stress with values that ranged from 2.3 to 185 dyne/cm2. The median shear stress of detachment of KG1a cells was directly related to the duration of membrane contact and the amount of immobilized monoclonal antibody (anti-CD34). The hollow-fiber assay provides a general method to determine functional properties of molecular domains that interact with cell surface receptors and markers.