Parallel Assessment of Th17 Cell Frequencies by Surface Marker Co-Expression Versus Ex Vivo IL-17 Production in HIV-1 Infection

Introduction: Th17 cells can either be identified by co-staining of surface markers or by intracellular cytokine staining (ICS) for IL-17 production. Discrepancies regarding the published frequencies of Th17 cells in peripheral blood mononuclear cells (PBMC) of HIV patients may partly be due to the different methodologies used. Methods: Cryopreserved PBMC from healthy controls and HIV-infected subjects, including treated (cART) and viremic patients, were split and analyzed side-by-side by flow cytometry for expression of surface markers CCR6, CXCR3, CCR4, and CD161, or for intracellular expression of IL-17A and IFN gamma after stimulation. Results: The characterization of Th17 cells as CXCR3-CCR6+CCR4+CD161+ yielded considerably higher frequencies than the corresponding frequencies obtained by characterization via cytokines (IL-17+IFN gamma-), regardless of the HIV status. However, the overall frequencies delivered by the two methods significantly correlated. The relative frequency of Th17 cells within the CD4+ T cell compartment was preserved in HIV infection but there was a significant decrease in the absolute Th17 number, which was restored after initiation of cART, paralleling CD4+ T cell recovery. Absolute Th17 numbers inversely correlated with HIV viral load. Conclusion: The definition of Th17 cells by surface markers might overestimate their frequency in comparison to functional assessment of IL-17 production by ICS, regardless of the HIV infection status. However, both methods yield proportionate results with reduced absolute numbers of Th17 cells in untreated HIV disease, reflecting the depletion of total CD4+ T cells in viremic HIV patients, and restoration with cART. (C) 2016 International Clinical Cytometry Society