Detection of intracellular cytokines in citrated whole blood or marrow samples by flow cytometry.

We have used three-color flow cytometric analysis for the detection of intracellular cytokines (IFN-gamma and IL-4) in CD3(+) cells, after stimulation for 4 h with phorbol 12-myristate 13-acetate (PMA) and ionomycin in the presence of monensin. We report in the present paper a validation study for analysing IFN-gamma and IL-4 production by bone marrow (BM)-derived T cells and peripheral blood T cells after BM transplantation. Using citrate as anticoagulant for blood and marrow sampling interfered with PMA+ionomycin-based cell stimulation. Indeed, removing this anticoagulant by two washes with 10% pooled human AB serum-supplemented RPMI 1640 before cell stimulation improved the percentages of IL-4(+) (0.02+/-0.01% to 0. 47+/-0.17% without and with washes, respectively; p<0.01) and IFN-gamma(+) (6.8+/-2.75% to 39.33+/-4.6%; p<0.01) cells to levels similar to those observed in heparin-based whole blood cultures (0.38+/-0.17% IL-4(+) and 34.27+/-4.96% IFN-gamma(+) cells; p>0.05). Delaying the cell cultures for 24 h did not significantly modify the detection of IFN-gamma in washed whole blood, but significantly altered IFN-gamma secretion in culture supernatants, as assessed by ELISA. Moreover, the percentage of IFN-gamma-producing cells within the CD3(+) lymphocyte population was stable, since similar results were obtained in two or three different independent experiments performed with the same healthy donors. This method was shown to be applicable for different kinds of citrated samples, such as blood or BM-derived cells. Overall, our data suggest that in addition to allowing for the identification of cytokine-producing cell phenotype, intracellular cytokines staining using flow cytometry is more reliable than ELISA for the biological follow-up of clinical samples.