In this assay using the Spike-RBD-mFC fusion protein binding to human cells expressing ACE2-EGFP, the confocal images obtained would likely show differences in the binding affinities between the D614 and G614 variants of the SARS-CoV-2 spike proteins.
If the binding affinity of the D614 variant is stronger, we would expect to see more intense and concentrated fluorescent signals in the confocal images. This would indicate a higher level of binding between the Spike-RBD-mFC fusion protein and the ACE2-EGFP receptors on the cell surface. The fluorescence would be localized around the areas where the fusion protein has successfully bound to the receptors.
On the other hand, if the binding affinity of the G614 variant is stronger, we would still expect to see intense and concentrated fluorescent signals. However, the distribution and localization of the fluorescence may differ compared to the D614 variant. The confocal images might show differences in the pattern or clustering of fluorescence, reflecting the binding characteristics of the G614 variant with the ACE2-EGFP receptors.
It's important to note that the specific appearance of the confocal images can vary depending on the experimental setup, labeling techniques, and imaging parameters. Therefore, the actual images obtained in the assay need to be analyzed and compared quantitatively to draw conclusions about the relative binding affinities of the D614 and G614 variants.