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IntroductionDendritic cells (DCs) are important for the initiation of immune responses to foreign antigens because of their "professional" competence to capture and present antigen to T cells. The 2 functions, antigen uptake and presentation, are temporally and spatially separated. Thus, after antigen internalization, the DCs themselves undergo a process of maturation, migration, and relocation (for review, see Bell et al 1 ). During maturation, DCs up-regulate major histocompatibility complex (MHC), adhesion, and costimulatory molecules, including CD80 (B7.1), CD86 (B7.2), CD54 (ICAM-1), CD58 (LFA-3), CD11a, CD11c, and CD40, whereas they down-regulate the expression of Fc and mannose receptors. 2 Mature DCs also secrete high levels of interleukin-12 (IL-12), a Th-1-polarizing cytokine that promotes the maturation of cytotoxic T cells (CTLs). 3 Several viruses, such as herpes simplex virus, 4 measles virus, 5 and Epstein-Barr virus, have been shown to diminish DC function. Recently, hepatitis C virus (HCV) infection has also been shown to affect the function of DCs. Compared to monocyte-derived DCs from healthy donors, DCs from patients with chronic HCV infection showed impaired ability to stimulate allogeneic T cells and to produce interferon ␥ (IFN-␥). 6 An independent study also demonstrated impaired stimulatory capacity of DCs derived from HCV-infected patients with hepatocellular carcinoma. However, this dysfunction was not unique to HCV because DCs from hepatitis B virus-infected patients with hepatocellular carcinoma also showed reduced stimulatory activity, suggesting that the liver damage itself might affect DC function. 7 These studies examined only the DCs of patients with chronic HCV infection. To the best of our knowledge, studies investigating DC derived from patients with cleared HCV infection have not yet been reported.Hepatitis C virus causes an often inapparent acute infection that is cleared only in a minority of patients. 8 Patients who are able to clear the virus mount a vigorous T-cell response. Spontaneous viral clearance is correlated with both HCV-specific, IFN-␥-producing CD8 ϩ T cells and a strong proliferative CD4 ϩ T-cell response during the first 6 months after infection. 9 Similarly, patients who cleared the virus mounted a CTL response to a larger number of viral epitopes than those who became chronic carriers. 10 In addition, persistent CTL activity could be detected in patients whose HCV was resolved but not in patients with chronic HCV infection. 11 The clearance of an HCV infection has also been correlated with a strong HCV-specific T-helper cell response. [12][13][14] Because DCs are essential for T-cell activation, we questioned whether viral clearance was affected by their abilities to process and present antigen. We therefore compared DCs from chronically infected patients to those from patients who cleared the virus after a course of antiviral therapy and to those of healthy donors. DCs were generated in a 2-step protocol. 15 First, monocytes were isolated from peripheral...