How Many Colors to Identify Regulatory T Cells in Humans

+ T cells can also express these markers. The number of parameters that can be scored simultaneously by multicolor flow cytometry has increased dramatically, through the development of new fluorescent dyes and tandems, providing a variety of excitation and emission spectra. Although a more polychromatic immunophenotyping generally corresponds to a more detailed Treg definition, most additional markers that are currently proposed for Treg identification are often expressed by activated conventional CD4 + T cells. Moreover, these analyses are both expensive and time consuming. Exploring typical Treg functions, i. e., anergy and suppressive capability with the intent to enumerate Tregs is difficult because of factors like Treg isolation, culture conditions, and the variable contamination of non-Treg populations in the assays. Functional assays are also cumbersome to set up and time consuming. We describe a simple flow cytometric assay that is based on the notion that Foxp3 and interleukin-2 expression is essentially mutually exclusive in Tregs.