A cell to cell adhesion assay was developed in order to examine the ability of membrane bound ACE or ACE2 to act as a ligand for cell adhesion. Cells over-expressing ACE or ACE2 or their mock transfected controls were used as cell adhesion substrates and Huh7 cells were labelled with BCECF fluorescent dye and allowed to adhere. Huh7 cell adhesion to the substrate cells was confirmed by immunofluorescence microscopy ( Figure 4A ). Calibrations confirmed that the relative fluorescence measured was proportional to the number of cells seeded ( Figure 4B ). A significant difference was seen between the adhesion of Huh7 cells to ACE2-expressing cells compared with non ACE2expressing cells ( Figure 4C ); the expression of ACE2 on the cell surface increased cell adhesion by approximately 25%. To further examine any role of RGD-mediated cell adhesion, cells were incubated with an RGD peptide prior to plating. Pre-incubation with RGD peptide significantly reduced the adhesion of Huh7 to HEK control cells ( Figure 4C ); cellular expression of ACE2 abolished the decrease mediated by pre-incubation with an RGD peptide ( Figure 4C ). Conversely, cellular expression of ACE conferred no enhanced adhesion properties compared to control cells ( Figure 4D ). In this model the presence of an RGD peptide reduced cellular adhesion by approximately 35% independent of tACE expression ( Figure 4D ).