The cytokine responses to cytomegalovirus (CMV) antigen in seropositive and seronegative individuals were measured using a combination of antigenic expansion and intracellular staining. Intracellular IFNgamma and IL-4 were produced in a dose-dependent manner by T cells in response to CMV only in the seropositive population. The potential for individual cells to produce both Th1 and Th2 cytokines simultaneously was clear, as IL-4 was most often produced in those cells with the highest IFNgamma production. The cytokine-specific nature of this response was demonstrated by fluorescence microscopy, which showed granular cytoplasmic staining, and at the mRNA level by ribonuclease protection assays. These methods expand our ability to evaluate the immune response to CMV, and can now be correlated to a number of clinical conditions.
