Differential production of IFN-γ, analyzed at the single-cell level, by specific subsets of human NK and T cells from healthy and HIV⁺ subjects

Background: Interferon gamma is a cytokine that plays a central role in immunity, and is physiologically secreted by T and NK cells under appropriate stimuli during the immune response. By means of flow cytometry, we performed a single cell analysis of interferon gamma producing NK cells and their surface phenotype in normal and HIV⁺ individuals that show several defects of cytokine production and cellular immunity. Methods: PBMC or purified NK cells were stimulated for 1-12 h with PMA/ionomycin in the presence of monensin, subsequently stained for surface CD56 and CD3 or CD8, and for intracytoplasmic IFN-γ, and analysed by flow cytometry. Results: Our results show that CD56⁺ NK cells are more efficient interferon gamma producers than T cells. Moreover, within the CD56⁺ NK cell population, those that co- express low density CD8 are the best producers. Finally, we show that NK cells during HIV infection are more massively recruited to interferon gamma production than those from normal subjects. Conclusions: Both in the normal and HIV⁺ subjects, a higher percentage of NK cells than T cells can produce IFN-γ although differences can be identified within the NK cells subset in terms of IFN-γ production. The production of IFN-γ is fully achievable in the HIV⁺ subjects, which is consistent with their elevated plasmatic levels of the cytokine. The possibility that NK cells that produce interferon gamma could represent a functionally distinct population committed to the production of this cytokine, is discussed. (C) 2000 Wiley-Liss, Inc.