Changing hepatitis C evades immune systems.

For the first time, researchers report that the human body produces antibodies against the hepatitis C virus. However, the rapidly mutating virus can outwit that line of defense to produce a chronic infection of the liver. The new findings hint at the difficulties in fashioning a vaccine that will shield people from multiple forms of this wily virus.

Patrizia Farci of the National Institute of Allergy and Infectious Diseases in Bethesda, Md., and her colleagues wanted to see if they could shield chimpanzees from the hepatitis C virus, a microbe that can cause a chronic inflammation of the liver.

Perhaps the least well known of the viruses that trigger this disease, hepatitis C can be spread through exposure to infected blood or body fluids, sharing needles with an infected person, and in some cases, transplantation of an infected organ (SN: 8/17/91, p.103).

The researchers reasoned that antibodies -- proteins made by specialized immune cells -- would circulate in the blood of an infected person. They therefore obtained plasma, the clear portion of blood, f rom a volunteer who had become infected with hepatitis C during a blood transfusion in 1977. (Blood is now screened for hepatitis C, and the risk of contracting the disease through a blood transfusion has declined.) The team also had access to the strain of virus infecting this patient during the acute phase of the illness.

In one experiment, the researchers injected a chimp with a strain of the acute-phase hepatitis C virus and with plasma collected from the volunteer in 1979. In the Aug. 2 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES, team members report that they blocked infection in this chimpanzee. Those findings show that the plasma obtained from the volunteer in 1979 contained antibodies that successfully neutralized the early form of the hepatitis C virus.

However, the researchers found they could not guard against hepatitis when they injected two other chimps with a mixture of the same virus and plasma taken from the recruit in 1990. At that point, the volunteer had already developed a chronic form of the disease. Scientists know that at least 50 percent of people infected with hepatitis C go on to suffer from this debilitating chronic disease, which can lead to liver cancer and death.

The virus present in the patient's blood in 1977 appeared very different from the virus recovered in 1990, the scientists found. Genetic analysis revealed that a section of the virus' outer coat differed by more than 28 percent between the 1977 strain and the 1990 strain.

These findings offer the reassuring news that the human body appears to manufacture protective antibodies against hepatitis C, at least at first.

The worrisome news is that hepatitis C appears to change so drastically that an effective vaccine may require a broad scope of action. Researchers will have to design a vaccine to protect against the early form of the hepatitis C virus as well as the later forms, perhaps a very difficult task.