A new study suggests that, contrary to current belief, the immune system eliminates most hepatitis B virus (HBV) without resorting to large-scale destruction of infected liver cells. A report of the study, conducted by National Institute of Allergy and Infectious Diseases (NIAID) grantees and scientists, appears in the April 30, 1999, issue of Science.
"This is an intriguing finding," notes NIAID Director Anthony S. Fauci, M.D. "By advancing our understanding of how HBV is cleared from the liver, it could lead to better treatments for HBV infection. It also sheds light on how the body protects against spread of an ongoing infection without destroying vital organs."
Scientists have thought that cell-killing T cells bring hepatitis B virus infections to an end by destroying infected liver cells. The current study, however, points to a noncytolytic process that targets the virus' ability to reproduce and leaves the liver relatively unscathed.
Luca G. Guidotti, D.V.M., Ph.D., and Francis V. Chisari, M.D., of the Scripps Research Institute in La Jolla, Calif., led the study, in collaboration with Robert H. Purcell, M.D., chief of NIAID's hepatitis viruses section, and other scientists. The researchers infected two healthy chimpanzees with HBV, then performed weekly blood and liver tests on the animals throughout the course of the infection.
The chimp HBV infections ran their course and the animals recovered without further complications. Most HBV infections in adult humans are similarly uncomplicated. However, between 5 and 10 percent of the estimated 320,000 new HBV infections in the United States each year become persistent, chronic infections. Annually, chronic HBV infection kills as many as 6,000 people in this country.
The researchers found the amount of hepatitis B virus DNA in the chimps' blood
and livers peaked eight weeks after infection. The HBV DNA levels then rapidly
decreased - by week 12 more than 90 percent of the HBV DNA
Contact: John Bowersox
NIH/National Institute of Allergy and Infectious Diseases