Regina H. Harley, M.S. Lab Supervisor - Flow Cytometry Facility Center for Vaccine Development University of Maryland - Baltimore 685 West Baltimore Street Baltimore, MD 21201 (410) 706-7376 FAX: (410) 706-6205 rharley@medicine.umaryland.edu >>> ttown <ttown@luna.cas.usf.edu> 07/31/00 12:18PM >>> The specific question is, do these percentages REALLY mean that out of 100 cells, x percentage express CD40? I tend to think that many more of those cells actually express CD40 but that such low expression levels of CD40 are undetectable by FACS. If this is the case, then what do these percentages really mean, and is there a reference(s) for this? Best wishes, Terrence Town This actually is a very good question and is relevant to any low incidence/low percentage molecule (where the incidence is the number of molecules per cell and the percentage is the number cells with the molecule). We are going to be working with a target that has both a low incidence and a low percentage. Due to a number of technical issues, the only fluorochromes we can use are PE and APC (and therefore can't use Molecualr Probes FITC amp. kit). Does anyone have a working system of amplification for these fluorochromes? We been trying various multistep procedures but have been having problems with high background. Any help/suggestions would be appreciated. Thanks very much. Regina
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