Even after compensation, background spread from spillover effects makes it difficult to determine appropriate gate boundaries. Positive and negative populations are not clearly separated in the detector of interest.
Common Causes
1Compensation removes spillover signals but does not correct background spread caused by spillover
2FMO (fluorescence minus one) controls not used to determine background from other fluorochromes
3Gate boundaries set without understanding cumulative background from all other channels
4High background from multiple fluorochromes accumulating in the target detector
Solutions
1Use FMO controls with all antibodies in the panel minus the one being measured to determine background spread
2Prepare FMO control for each detector where gate boundary is difficult to establish
3Analyze FMO data to understand background contribution from all other fluorochromes in the target detector
4Set appropriate gates based on FMO control data showing cumulative background effects