I have a problem with the detection of a GPCR by flow cytometry.

Using a PE labelled antibody either directly or indirectly using a secondary antibody, I get a nice signal. Because we introduced RFP I need to switch to another channel. However, using the same directly labelled antibody either labelled with PE/Cy5 or Cy7 or using secondary antibodies labelled with these dyes we do not get any signal!

The cell line we use is several times shown to be positive and we can reproduce this as shown above. What is wrong? Does anybody have a solution? By the way, we are using a FACS Calibur.

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