The immigration of 25,000 Ethiopians to Israel three years ago provided more than a boost to the Jewish population. It set the stage for Israeli doctors to say a "natural immunity" to AIDS exists.

In analyzing the cases of Ethiopians who immigrated to Israel, Dr. Zvi Bentwich found 50 percent had been exposed to the HIV virus but tested negative for AIDS. It appears their bodies developed an immunity to the disease.

And that fact, he says, is the next step building block to developing a vaccine to fight the deadly disease.

At the recent ninth International Congress of Immunology in San Francisco, Bentwich, a professor at the Hadassah-Hebrew University School of Medicine in Jerusalem, which is associated with Kaplan Hospital in Rehovot, presented the findings that back up hopes for a vaccine.

"What this means," Bentwich said, "is that we know how to improve the course of the disease and that the prospect of a vaccine is positive."

When Ethiopians first began arriving in Israel, 90 percent of them were infected with some sort of virus, with 2 percent testing positive for AIDS. Bentwich tracked the health and treatment of all viral carriers from their first day on Jewish soil.

Besides finding that half the Ethiopian Jews were exposed to the virus but did not develop it, he noticed the disease behaved differently in Israel than in Africa. This suggests that environmental factors may affect the course of the illness.

In Africa, Ethiopians infected with HIV died two to three times more quickly than those infected in the West.

In addition, the heightened prevalence of various infections in Africa yielded increased exposure to sickness and a greater likelihood of falling prey to the AIDS virus. However, the Ethiopians' immune systems responded by kicking into high gear or increased activity, Bentwich said.

Three years later, with the help of medicine and a new environment free of African diseases, most non-AIDS and HIV viruses have been eradicated from the Ethiopian-Israeli population. Their immune systems returned to normal and the progression of AIDS in those already infected slowed down.

"What this suggests is that a change of environment affects the immune system and determines how the disease behaves," Bentwich said. In people with AIDS, "the infection increases the susceptibility to other diseases, which aggravate the AIDS virus" and shortens the time between infection and death.

Bentwich said this complements a controversial theory he voiced 10 years that gays, at that time, were more prone to AIDS — " a very unpolitically correct" observation, he said.

He asserted that the immune systems of gay men were weaker due to a promiscuous and drug-abusive lifestyle that was common prior to the discovery of AIDS. So gays, like Ethiopians, were more susceptible to a host of diseases, including AIDS.

However, "they made changes in lifestyle and sexual habits, and lowered their incidence of all diseases," especially AIDS, he added.

To date, about 1,600 Israelis officially have tested positive for AIDS. Bentwich estimates the number is closer to 3,000. Approximately 400 of those infected are Ethiopian immigrants, roughly about the same number as three years ago.

These numbers, Bentwich said, affirm his suspicions that HIV was not lying dormant in the Ethiopians exposed to, but testing negative for, the AIDS virus. And it suggests, "the development of a natural immunity," he added.

However, many doctors and professors are skeptical about the prospect of a natural immunity for AIDS.

"They say, `Wait, the virus is hidden.' But, we've followed these individuals for several years and they still have not developed the [AIDS] virus or the antibodies," Bentwich said, adding that American and European studies have yielded similar results.

"The phenomenon we're seeing of exposure without infection isn't the first. It's not so controversial. The major issue is, how do we learn from it?"

While Bentwich cautioned that is too early to discuss the possibility of a cure for AIDS, he said the findings in Israel point to "one day developing a vaccine."