All patients gave informed consent with Protein Tyrosine Kinase inhibitor approval by the relevant ethics committees as previously described. 8, 10 and 17 Patients were excluded if they were human immunodeficiency virus positive or hepatitis B virus surface antigen positive. The patients are classified into the following 3 cohorts: (1) exposed uninfected (EU) cohort, (2) spontaneous resolving (SR), and (3) chronically infected individuals. Seventy-four individuals were recruited from Dartmoor Prison, needle exchanges, community drug services, and hostels in Plymouth, United Kingdom. All these individuals were of Caucasian ethnicity. They had

an extensive history of past or present injection drug use. This group was defined as being both HCV antibody (third generation enzyme linked immunosorbent NVP-BGJ398 assay, Abbott IMx, Abbott Diagnostics, Maidenhead, Berkshire, United Kingdom) and HCV RNA (Amplicor, Roche Diagnostics, Pleasanton, CA) negative on at

least 2 occasions, 3–6 months apart with subsequent testing on an approximate 6 monthly basis to ensure that this profile remained unchanged. Forty-two of these cases had been genotyped previously for KIR2DL2/3 and HLA-C.10 Detailed information about drug injecting behavior was ascertained by means of a structured questionnaire, and the median duration of intravenous drug use was 8.62 ± 6.05 years (range, 0.3–24) with a median number of injections of 4927 (range, 36–41,620).10 Their median age was 28 years, and 64 (79%) were male. SRs. Individuals were classified in this group if they had detectable anti-HCV by second-generation enzyme-linked immunosorbent assay (Abbott IMx; Abbott Diagnostics, Maidenhead, Berkshire, United Kingdom) and no detectable HCV viremia by Quantiplex HCV RNA 2.0 assay (Chiron, Emeryville, CA)

or HCV COBAS Amplicor system (Roche Diagnostics, Pleasanton, CA) on at least 2 occasions 6 months apart. They were recruited between 1995 and 1998 as part of the Hepatitis C European Network for Cooperative Montelukast Sodium Research (Hencore) collaboration17 and 18 and between 1999 and 2005 from Addenbrookes Hospital, Cambridge, United Kingdom, and Southampton General Hospital, United Kingdom.8 Eighty-seven (98%) were Caucasian, 59 (66%) were male, and their median age was 36 years. Forty-four had been genotyped previously for KIR2DL2/3 and HLA-C. 8 These individual were all persistently anti-HCV and HCV RNA positive, by second-generation enzyme-linked immunosorbent assay (Abbott IMx) and HCV COBAS Amplicor system (Roche Diagnostics, Pleasanton, CA), respectively. They were recruited from the general hepatology clinic at Southampton General Hospital, United Kingdom, between 2003 and 2007. Two hundred seventeen (93%) were of Caucasian origin, with a median age of 45 years, and 138 (59%) were male.10 All had been genotyped previously for KIR2DL2/3 and HLA-C.