The use of pepsin in receptor internalization assays.

For internalization experiments that use fluorescent antibody (Ab) staining to distinguish between inside versus outside cellular localization of various receptor targeting ligands, it is critical that there be efficient removal of all residual surface-bound fluorescent Ab. To achieve this, a fluorescent Ab removal technique is commonly employed in receptor internalization assays that utilizes low pH glycine-based buffers to wash off the residual non-internalized fluorescent Ab retained on cell surfaces. In this study, we highlight the shortcomings of this technique and propose an alternative in situ proteolytic approach that we found to be non-deleterious to the cells and significantly more effective in removing the residual fluorescence resulting from non-internalized surface-bound Ab.