Gamma Interferon Expression in CD8+T Cells Is a Marker for Circulating Cytotoxic T Lymphocytes That Recognize an HLA A2-Restricted Epitope of Human Cytomegalovirus Phosphoprotein pp65

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Abstract
Antigen-specific CD8+T cells with cytotoxic activity are often critical in immune responses to infectious pathogens. To determine whether gamma interferon (IFN-γ) expression is a surrogate marker for cytotoxic T lymphocytes (CTL), human cytomegalovirus-specific CTL responses were correlated with CD8+T-cell IFN-γ expression determined by cytokine flow cytometry. A strong positive correlation was observed between specific lysis of peptide-pulsed targets in a51Cr release assay and frequencies of peptide-activated CD8+T cells expressing IFN-γ at 6 h (r2= 0.72) or 7 days (r2= 0.91). Enumeration of responding cells expressing perforin, another marker associated with CTL, did not improve this correlation. These results demonstrate that IFN-γ expression can be a functional surrogate for identification of CTL precursor cells.