Effect of dendritic cells on flow cytometric quantification of cytomegalovirus-specific, interferon-γ-producing T cells

Flow cytometric measurement of intracellular cytokines in T cells exposed to antigen is a widely used method for quantification of an antigen-specific T-cell response. As the frequency of antigen-specific T cells is often very low, any improvement in signal to noise ratio is of great importance. Thus, in this study, the ability of antigen-pulsed dendritic cells (DCs) to increase the number of antigen-specific, interferon-gamma (IFN-gamma)-producing CD4(+) T cells measurable both in fresh peripheral blood and in reconstituted frozen blood mononuclear cell (MNC) samples was evaluated. Cytomegalovirus (CMV) was used as antigen in a 10 h assay, using cells from both CMV-seropositive and -seronegative donors. When reconstituted frozen samples were analysed, the general response towards CMV lysate in CMV-seropositive donors was 23-86% lower compared to the corresponding fresh blood samples. Antigen-pulsed DCs could not improve the sensitivity of the intracellular cytokine-detection assay when fresh peripheral blood samples were used. Interestingly, however, the addition of CMV lysate-pulsed DCs to cryopreserved MNC samples substantially increased the frequency of specifically induced IFN-gamma-producing cells to a level comparable to the frequency found in the corresponding fresh blood samples.