Quantification of immunosuppression by flow cytometric measurement of intracellular cytokine synthesis.

The availability of a method to measure the effects of drugs on immune reactivity should be helpful in optimizing treatment after organ transplantation. Since cyclosporine A (CSA) interferes with activation of T cells and cytokine synthesis, production of IL-2 and IFN-gamma might constitute a marker of this drug's effects. We measured the capacity for mitogen-stimulated production of these cytokines in whole blood by using immunostaining of intracellular and membrane antigens, followed by flow cytometry. The percentage of CD4+ T cells producing IL-2 or IFN-gamma was strongly reduced in 20 transplant patients compared with 24 healthy controls. The capacity for IL-2 production of CD4+ and CD8+ cells correlated inversely with CSA blood levels (P values 0.0087 and 0.0396, respectively). IFN-gamma production by CD4+ T cells showed a negative correlation with the prednisolone dose (P = 0.0175) and, for the CD8+ subset, with CSA trough levels (P = 0.0023). These data show that inhibition of T cell cytokine synthesis by CSA and prednisolone can be quantified.