Hello All, A couple last questions about PI staining for viability. I have found that very often there is a population of lower intensity PI as well as the very high one that we typically define as dead. I think there are logical explanations for the presence of this, but the problem is how can you get away without using a dedicated detector for PI and be sure that some of what you are assuming to be, for instance, positive PE or PE/CY5 is not actually low intensity PI? I have also seen, even with preparations that have been washed after the addition of PI, an increase in the background of the PE signal. I'm not really sure why this happens, but do people just ignore it? Wouldn't it cause as much problem with samples of not extremely bright, and relatively rare, positive populations as would a few, maybe less than 1%, non-specifically staining dead cells? And you can't really compensate it away. These things have nagged me for a long time. I hope someone can offer some advice. Thanks, Cheryl
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