Re: Strange signal shift
This is a very interesting problem, thank you for sharing. I think Mike’s comment about debris binding antibodies preferentially is the most probable scenario to fit this channel specific drift over time. I would speculate there are debris particles that are positive for one or more of your 4 drift channels that are aggregating onto your cells over the 1h run.
With your current data set, you could gate on the first 5 minutes of your 1h run when the signal is low, then on the last 5 minutes during the peak of the drift. Then compare the frequency of DNA- events that are also positive for the markers in your drifting channels for these two time windows. If this is being caused by debris aggregating to your cells I would expect to see the frequency of DNA-, drift channel+ (148Nd, 150Nd, 152Sm or 154Sm) events per 5 minute window decrease towards the end of the run as they adhere to DNA+ cells over time (assumes a constant sample introduction rate).
If you were to encounter this again I would suggested pausing the run, more aggressively mixing the cell suspension, then filtering (35 micron nitex) before resuming to see if that corrects the drift you're seeing.
Please keep us updated, I’m curious to know the cause.
-Greg
UHN/Sickkids FCF
Toronto, Canada