Expression of the chemokine MIG is a sensitive and predictive marker for antigen-specific, genetically restricted IFN-gamma production and IFN-gamma-secreting cells

The evaluation of antigen-specific immune responses is critical for underst anding the mechanisms of immune protection and for establishing the efficac y of candidate vaccines. Here, we describe a novel assay for IFN-gamma acti vity which is based on the flow cytometric detection of the chemokine, mono kine induced by gamma interferon (MIG) as a sensitive and predictive measur e of IFN-gamma -mediated effector function, and a surrogate marker for IFN- gamma -producing cells. Upregulation of MIG expression was demonstrated fol lowing in vitro activation of peripheral blood mononuclear cells (PBMCs) wi th defined CD8(+) T-cell epitopes derived from influenza virus, cytomegalov irus (CMV), or Epstein-Barr virus (EBV) and was antigen-specific, genetical ly restricted and dependent on both CD8(+) T cells and IFN-gamma. Furthermo re, antigen-specific MIG expression was also demonstrated with Plasmodium f alciparum circumsporozoite protein (CSP) peptides, using PBMCs from volunte ers immunized with irradiated P. falciparum sporozoites. In multiple parall el experiments, the MIG assay was compared to conventional IFN-gamma ELISPO T, IFN-gamma ELISA, MIG ELISA and intracellular cytokine staining assays. T he level of MIG expression was shown to be directly associated with the num ber of IFN-gamma spot-forming cells (SFCs) detected by ELISPOT (r(2) = 0.94 ). Moreover, in all instances where cultures were considered positive by EL ISPOT, a higher stimulation index was noted with the MIG assay as compared with the ELISPOT assay (on average at least threefold higher) and, in some cases, responses as detected by the MIG assay were significant, but the cor responding response as measured by ELISPOT was not significant. Finally, th e flow-based MIG assay offers a number of practical and technical advantage s over the ELISPOT assay. Our data validate this novel method for the detec tion of low as well as high levels of antigen- specific and genetically res tricted IFN-gamma activity. Published by Elsevier Science B.V.