An immunomodulatory role for CD4+CD25+ regulatory T lymphocytes in hepatitis C virus infection

<jats:sec> <jats:title/> <jats:p>The CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> regulatory T lymphocytes have been implicated in suppressing T cell immune responses. Our aim was to characterize the frequency, phenotype, function, and specificity of CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> T cells in hepatitis C virus (HCV) infection. Peripheral CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> cells from recovered (n = 15), chronic infected (n = 30), and normal control (n = 15) subjects were analyzed <jats:italic toggle="yes">ex vivo</jats:italic> for quantitation, phenotype, and effect on HCV-specific interferon gamma production and proliferation. CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> specificity was determined by intracellular cytokine staining for interleukin 10 (IL-10). A higher proportion of CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> were found in chronic infection (mean, 3.02%) when compared with recovered (1.64%, <jats:italic toggle="yes">P</jats:italic> = .001) and normal controls (2.27%, <jats:italic toggle="yes">P</jats:italic> = .02). CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> cells display CD45RO<jats:sup>high</jats:sup>, CD45RA<jats:sup>low</jats:sup>, CD28<jats:sup>high</jats:sup>, CD62L<jats:sup>high</jats:sup>, and CD95<jats:sup>high</jats:sup> phenotype. HCV-specific interferon gamma activity was enhanced in peripheral blood mononuclear cells depleted of CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> and suppressed in peripheral blood mononuclear cells enriched with CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup>. Depletion of CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> cells also enhanced HCV-specific CD4<jats:sup>+</jats:sup> and CD8<jats:sup>+</jats:sup> T cell proliferation. Cytokine analysis suggested CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> cells secrete transforming growth factor beta (TGF-β<jats:sub>1</jats:sub>) and IL-10. The inhibitory role for TGF-β<jats:sub>1</jats:sub> was confirmed by anti-TGF-β<jats:sub>1</jats:sub>. Transwell studies showed CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> mediated suppression to be dose dependent and requiring cell contact. CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> cells showed HCV-specificity through IL-10 production, with a frequency ranging from 1.9% to 5.3%. A positive correlation was detected between CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> T cell frequency and HCV RNA titer, whereas an inverse relation was found with liver inflammatory activity. <jats:underline>In conclusion,</jats:underline> CD4<jats:sup>+</jats:sup>CD25<jats:sup>+</jats:sup> T lymphocytes constitute a highly differentiated population and appear to play a role in viral persistence by suppressing HCV-specific T cell responses in a cell-cell contact manner. (Hepatology 2004;40:1062-1071.)</jats:p> </jats:sec>