I received a generous amount of replies to my question. Here is a summary of the responses. Thanks to all those who replied. Have a good weekend! Maciej 1 - freezing cells prior to acquisition: AGB writes that frozen cells' fluorescence is retained but the light scatter 'morphology' may look messy (I confirmed this in our lab) MWL "If PBMCs really are PBMC preps and not the results of a lysed whole blood procedure, you can fix the labelled cells with 1% paraformaldehyde and store at 4oC for several months (the original FACS QA programs used such preparations very successfully)." HT "Your stained specimens will not survive freezing. Better to store them at 4C. Keep them from being exposed to light as much as possible. They should be stable for a week that way. If you don't have Na-azide in the storage buffer (PBS) and they're kept warm, the membrane bound antibody will be endocytosed, and you'll lose detection capability. If stored refrigerated over the weekend, analysis on Mon should not be a problem." TB "It is much better to fix the cells after staining in 1-2% paraformaldehyde. This will stabilize the cells for several days. They should be fixed for at least an hour before analyzing." SM "Are you using decent quality fresh formaldehyde? If you use EM grade and make it up fresh there shouldn't be much change over a few days. Polyscience and Tousimis make EM grade formaldehyde in handy glass vials.You can also fix for an hour or two then wash out and suspend your cells in PBS. Freezing sounds like a lot of trouble." 2 - can I reuse antibodies that have been sitting in tubes for a while? PB "trash and don't do again" MWL "you'll almost certainly need to throw them away as the fluorochrome is likely to have become detached from the mAb."
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