Manuela Benary (email@example.com)
Hanna Bendfeldt (firstname.lastname@example.org)
Ria Baumgrass (email@example.com)
Hanspeter Herzel (firstname.lastname@example.org)
 Institute for Theoretical Biology, Humboldt University of Berlin, Invalidenstr. 43, 10115 Berlin, Germany
 German Rheumatism Research Centre, Chariteplatz 1, 10117 Berlin, Germany
Interleukin-2 (IL-2) is one of the first cytokines to be expressed by T helper cells (Th cells) after antigen-specific stimulation. In contrast, regulatory T cells (Treg cells) do not express IL-2, although they are activated via the same pathways. In regulatory T cells the additional transcription factor FoxP3 is expressed. Using intracellular measurement of the transcription factors NFAT and FoxP3 as well as the cytokine IL-2 on single cell level we revealed a small fraction of IL-2 expressing Treg cells. Furthermore, these data enabled us to develop initial mathematical models describing gene expression of IL-2 in individual cells. The models are adapted to data from human regulatory T cells. Based on statistical tests of available flow cytometric data it seems reasonable that not only the amount of the transcription factors NFAT and FoxP3 is important but also their concentration ratio. We discuss specific problems of modeling gene expression on single cell level taking IL-2 expression as an example.