Effects of age and viral determinants on chronicity as an outcome of experimental woodchuck hepatitis virus infection

Abstract

Acute hepadnavirus infections either resolve or progress to chronicity. Factors that influence chronicity as an outcome of hepatitis B virus (HBV) infection in humans can be studied experimentally in the woodchuck model. Accordingly, several woodchuck hepatitis virus (WHV) inocula were characterized. Representative inocula had high titers of infectious virus (approximately 10 7.7 -10 9.5 woodchuck 50% infectious doses per milliliter [WID 50% /mL] by subcutaneous inoculation), with 1 WID 50% ranging between 21 and 357 physical virion particles. WHV7P1 (standard high dose, 5 ؋ 10 6 WID 50% ) produced a 72% chronicity rate (i.e., percent chronic of total infected) in neonatal woodchucks (1-3 days old). Comparable doses of WHV8P1 resulted in a lower chronicity rate in neonates (34% chronic) indicating that it represented a strain different from WHV7P1. Neonatal woodchucks were more susceptible to chronic infection by high doses of WHV7P1 (range, 65%-75% chronic) compared with 8-week-old weanlings (33% chronic) and adult woodchucks (0% chronic; i.e., all resolved). High doses of cloned wild-type viruses also induced high rates of chronicity in neonates (70%-80% chronic). Chronicity rates in neonates were decreased for low doses of WHV7P1 (500 WID 50% , 9% chronic) and for high doses of a precore WHeAg-minus mutant WHV8 clone (17% chronic). Thus, both age and viral determinants can influence chronicity as an outcome of experimental WHV infection. Standardized inocula will enable the study of mechanisms that initiate and maintain chronic hepadnavirus infection and also provide a means for developing WHV carriers for therapeutic studies. (HEPATOLOGY 2000;31:190-200.)The eastern woodchuck is naturally infected by a virus closely related to hepatitis B virus (HBV). Experimental infection of woodchucks with woodchuck hepatitis virus (WHV) has been of value in modeling virtually all aspects of HBV infection, pathogenesis, and therapy. 1,2 Development of the model has evolved to use woodchucks bred and reared under controlled environmental conditions, virus-and hostspecific assays for viral infection and disease, and standardized WHV inocula. Because titered HBV inocula have proven invaluable for developing the chimpanzee as a predictive model of HBV infection, disease, and vaccine protection, 3 titered WHV inocula were considered essential for further defining host and viral determinants that promote chronicity and disease progression to hepatocellular carcinoma (HCC) in hepadnavirus infection. In this study, we measured the infectivity of several WHV inocula and, using controlled doses of virus, showed that both animal age and viral determinants can affect chronicity as an outcome of WHV infection. These standardized inocula represent a useful resource for developing serum and tissue banks from selflimited and chronic WHV infections for studies of WHV pathogenesis, and for producing chronic carrier woodchucks at predictable frequencies. MATERIALS AND METHODSAnimals. Woodchucks were bred, maintained, and handled under contr...

Pathogenesis of experimental neonatal woodchuck hepatitis virus infection: Chronicity as an outcome of infection is associated with a diminished acute hepatitis that is temporally deficient for the expression of interferon gamma and tumor necrosis factor-alpha messenger RNAs

“…19 Our conclusion was possible from selected comparative measurements in stored liver tissues 19 from 2 early time points that were chosen based on our experience with infections in this model. [17][18][19] In adult WHV infections, viremia can be detected as early as 2 to 3 weeks postinfection, peak at weeks 6 to 8, and wane by weeks 10 to 12. 7,17 In typical neonatal infections involving WHV7P1, 18 week 8 represents a comparative baseline state for both outcomes.…”

“…19 Briefly, neonatal woodchucks born to WHV-negative dams were inoculated subcutaneously at 3 days of age with 5 ϫ 10 6 woodchuck 50% infectious doses of WHV7P1. 18 Uninoculated neonatal woodchucks were used as age-matched uninfected controls. The surgical sampling protocol for liver tissues (and paired blood samples) was designed as a 2 ϫ 3 factorial experiment involving 2 time points and 3 experimental categories (i.e., 6 independently sampled groups 19 ).…”

“…Results for these acute phase parameters were grouped and compared with respect to the outcome of infection determined serologically at 1 year postinfection (i.e., chronic vs. resolved). 18,21 Isolation of Total Liver RNA. Total RNA was extracted from 100 to 400 mg pieces of liver as described previously.…”

“…Therefore, characterization of the early response mechanisms leading to chronicity in neonatal infection is important to the goal of developing rational immunotherapies. Experimental infection of neonatal woodchucks with the woodchuck hepatitis virus (WHV) [16][17][18] is being used to compare acute phase responses associated with chronic versus self-limited outcomes. In a previous study, 19 blood and surgical biopsy specimens of liver were obtained from neonatally infected woodchucks during the acute phase before the outcomes became obvious by serologic classification.…”

Hepatitis B e antigen–negative chronic hepatitis B

“…12 The first possibility has been quickly ruled out on the basis of clinical 12 and experimental 41 data showing that in contrast to acute HBV infection with wild-type HBV, de novo precore mutant HBV infection rarely, if ever, goes into chronicity. Infants born to HBeAg-negative mothers 12 and adults acquiring HBV from HBeAg-negative infected individuals 42 do not develop chronic HBV infection.…”