Hepatitis C virus is both difficult to treat and a significant cause of morbidity and mortality. It is not understood how hepatitis C establishes infection nor how some patients clear infection. To this end 83 humans exposed to hepatitis C were studied in protocol 00-DK-0221. The immune response (both antibody and T cell) was closely followed and is being characterized. The study is in collaboration with Dr. Rehermann. As an extension of this 28 patients with acute hepatitis C have been followed and treated as indicated. Twenty-five patients (16 women;mean age 43 years) had adequate follow up to be included in an analysis. Symptoms in the acute phase were reported by 80% and jaundice by 40%. Two patients (8%) developed ascites and acute liver failure but both survived. Genotype 1 was most frequent (72%) but many patients (20%) could not be genotyped. Serum aminotransferase levels and HCV RNA levels fluctuated greatly;18% of patients were intermittently negative for HCV RNA. In follow up, 5 patients recovered spontaneously whereas 20 developed chronic hepatitis C or received interferon-based therapy during the acute phase. Among 15 patients treated during the acute phase with peginterferon with or without ribavirin for 24 weeks, all became HCV RNA negative within 4 to 8 weeks, and all except two achieved a sustained virological response with the exceptions being HIV-positive. Side effects (particularly psychiatric) were common and limited the duration of therapy in 30% of patients. To further understand the virological determinants of infection and the development of chronicity, the hepatitis C virus sequence in the early stages of infection has been determined from the same patients. In particular the sequencing effort is focused on the viral sequence before and after treatment, in the two patients who were HIV positive and relapsed. The complete sequence has been determined and is now being analyzed. A second laboraratory project has been to study the nature of late relapse after treatment for hepatitis C. The first 103 patients who achieved a sustained virologic response at the National Institutes of Health Clinical Center were reviewed. Three patients had a late relapse. The viral sequence from these patients was studied from before treatment, from the liver at the time of sustained virologic response, and from the serum at the time of documented relapse. The viral sequences obtained from before treatment, the liver at the time of sustained virologic response, and from the serum at the time of relapse were all virtually identical proving relapse and not reinfection. A third laboratory project currently underway is to use viral sequencing to understand discrepancies in commercial genotyping assays. A collaborative project with Drs. Natanya Sandler and Danny Doueck was to determine the relationship between markers of microbial translocation and chronic liver disease. We investigated whether the extent and progression of liver disease in patients with chronic HBV or HCV infection are associated with microbial translocation and subsequent activation of monocytes. In a retrospective study, we analyzed data from 16 patients with minimal fibrosis, 68 with cirrhosis, and 67 uninfected volunteers. We analyzed plasma levels of soluble CD14 (sCD14), intestinal fatty acid binding protein, and interleukin-6 by enzyme-linked immunosorbent assay, and lipopolysaccharide (LPS) by the limulus amebocyte lysate assay, at presentation and after antiviral treatment. Compared with uninfected individuals, HCV- and HBV-infected individuals had higher plasma levels of LPS, intestinal fatty acid binding protein (indicating enterocyte death), sCD14 (produced upon LPS activation of monocytes), and interleukin-6. Portal hypertension, indicated by low platelet counts, was associated with enterocyte death (P = .045 at presentation, P <.0001 after therapy). Levels of sCD14 correlated with markers of hepatic inflammation (P = .02 for aspartate aminotransferase, P = .002 for ferritin) and fibrosis (P <.0001 for &#947;-glutamyl transpeptidase, P = .01 for alkaline phosphatase, P <.0001 for &#945;-fetoprotein). Compared to subjects with minimal fibrosis, subjects with severe fibrosis at presentation had higher plasma levels of sCD14 (P = .01) and more hepatic CD14(+) cells (P = .0002);each increased risk for disease progression (P = .0009 and P = .005, respectively). LPS-induced local and systemic inflammation is associated with cirrhosis and predicts progression to end-stage liver disease in patients with HBV or HCV infection. A second type of chronic hepatitis studied is hepatitis D. Hepatitis D is the most aggressive form of viral hepatitis as well as the most difficult to treat. Interferon therapy is the standard approach. Patients are typically treated for 6 months to a year. Relapse after cessation of therapy is the norm. In protocol 01-DK-0247 patients are treated with peginterferon for 5 years. The dose is titrated to maintain normal ALT and minimize side effects. Patients are evaluated before initiating therapy, and after 1, 3, and 5 years. Patients are excluded if they do not meet protocol-defined criteria for response at the 1 year evaluation. Enrollment was planned for 10 - 20 patients. Thirteen patients have been enrolled, and of the 12 who have had one-year evaluations 10 have met the protocol definition of response. Most of the patients were male (11) and tended to have advanced disease (median baseline Ishak fibrosis - 4). Patients were treated for a mean duration of 144 weeks (range 6 - 300) at an average weekly peginterferon dose of 184 &#956;g. At one year of treatment, inflammatory scores were significantly improved (10.6 2.7 vs. 7 1.9, p<0.01) and this improvement persisted in 4 of 5 patients who had a 3 year biopsy scored. There was no difference in the fibrosis score. ALT decreased significantly after one year (136 143 vs. 46 13, p<0.05) and persistant biochemical response on treatment was achieved by 3 patients (27%). 3/13 patients (27%) lost HBsAg after 24, 37 and 202 weeks of treatment and developed HBs antibodies. Treatment was stopped in these patients at least 24 weeks later;the serological response was durable and was associated with persistent improvement of ALT and platelet count during follow-up. Two patients (15%) died during therapy, one from hepatocellular carcinoma and the other from herpes colitis. Both deaths were not considered related to treatment. There were no other serious adverse events and treatment was well-tolerated overall. 3 patients required a dose reduction due to cytopenias. The primary end point of the study is the evaluation after three years although it is planned to treat patients for 5 years. Hepatitis D viral RNA and hepatitis B surface antigen levels have been measured, the final analysis is currently being completed.