Cytokine flow cytometry: understanding cytokine biology at the single-cell level.

In the past 4 years, cytokine flow cytometry has emerged as the premier technique for enumeration of cytokine producing T cells. The multiparameter capability of flow cytometry permits the simultaneous detection of two or more cytokines within a single cell, allowing true Th1 vs. Th2 determination. The high throughput inherent to flow cytometry has enormous advantages when applied to clinical research questions previously not amenable for study using labor intensive techniques such as ELISPOT, limiting dilution and T cell cloning. Furthermore, cytokine flow cytometry allows the study of individual T cells directly ex vivo, minimizing artifacts due to long term culture. As such, cytokine flow yields unique insights into cytokine biology heretofore not possible. We have used cytokine flow cytometry to examine coexpression of cytokines within the memory/effector CD4+, CD27- subset. Doing so, we have found distinct cytokine producing subsets that correlate with the previously described Th1, Th2 and Th0 subsets. The majority of cytokine producing cells were of these first two subsets with fewer cells coexpressing IFN-gamma and IL-4. These results validate the Th1/Th2 hypothesis and demonstrate specific subsets of cytokine producing T cells in fresh ex vivo human T cells.