IL-2 or IL-4 mRNA as a potential flow cytometric marker molecule for selective collection of living T helper 1 or T helper 2 lymphocytes.

Flow cytometry has been widely used to analyze and sort out particular types of living cells that have specific marker molecules. In many cases, marker proteins are present on the cell surface and are detected by monoclonal antibodies against them. However, there are some cases in which cells do not have specific marker molecules on their surface. In this situation, it would be useful if mRNA that is expressed specifically in the particular cell could be used as a marker molecule. We previously reported that mRNA can be detected in living cells by hybridizing a pair of fluoreophore (donor or acceptor)-labeled oligonucleotides to adjacent locations on the target mRNA in the cytoplasm of cells (Tsuji, A.; Koshimoto, H.; Sato, Y.; Hirano, M.; Sei-Iida, Y.; Kondo, S.; Ishibashi, K. Biophys. J. 2000, 78, 3260-3274). On the formed hybrid of the two fluorescent oligonucleotides with the target mRNA, the distance between the two fluorophores becomes very close, which results in fluorescence resonance energy transfer (FRET). Combining this fluorescent labeling method for mRNA with flow cytometry, we have examined the isolation of living CD4+ T helper lymphocytes expressing IL-2 mRNA (Th1) or IL-4 mRNA (Th2). A pair of fluorescent oligonucleotides for hybridizing to IL-2 or IL-4 mRNA were introduced into activated CD4+ T lymphocytes by electroporation. The cells were applied to FACS and analyzed by FRET signals. Th1 or Th2 lymphocytes were exclusively sorted from their mixed populations in activated CD4+ T cells. Our results demonstrate that it is possible to use mRNA as marker molecules to analyze and isolate living cells in flow cytometry.