Scientists searching through human genetic material for potential drugs reported yesterday that they had found a protein that stimulates the immune system to produce more antibodies, critically important in fighting off many types of germs.

Scientists at Human Genome Sciences Inc. (HGS) of Rockville described the protein in today's edition of the journal Science. In interviews, they said the potential medical implications of the discovery are quite broad, from fighting various types of immune deficiency to making improved vaccines to combating cancers that arise from cells of the immune system.

Proving that the new discovery will be useful for any of these purposes will take years, but a top government scientist not involved in the work said yesterday that it holds significant medical potential. "I think it's very important," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda. He noted that the new protein seems to target only the cells that make antibodies, a feature that could reduce potential side effects and heighten its usefulness.

The new protein stimulates the growth and activity of B lymphocytes, the principal immune cells responsible for making antibodies. Antibodies are proteins that latch on to such foreign invaders as bacteria or viruses in an attempt to neutralize them. HGS scientists have dubbed the new protein BLyS, for B Lymphocyte Stimulator.

They are not the first group to describe the protein -- at least two other papers have been published this year. But they are the first scientists to report that BLyS actually works in animals to stimulate the immune system, a critical finding. Moreover, the HGS scientists appear to be ahead of rival groups in securing patent rights on the protein.

By stimulating B cells to divide and rev up their production of antibodies, BLyS "increases the number of soldiers and the number of bullets they can shoot at any one time," said David Hilbert, an HGS scientist who led the work with his colleague, Paul Moore. "It enhances the function dramatically."

Some important inherited diseases involve antibody deficiencies, and many AIDS patients develop similar deficiencies as their immune systems weaken. BLyS offers a possible treatment option for such patients.

In addition, scientists said it is possible the protein could be used to prime the immune system in advance of a vaccination. Conceivably, this might permit vaccination against malaria, tuberculosis, AIDS or other diseases for which vaccine research has been disappointing. Vaccines work largely by stimulating antibodies against a germ.

Less directly, the scientists said, BLyS could light a path toward combating certain cancers. Once scientists learn how to stimulate cells, they can often apply that knowledge in reverse to devise ways to slow down the cells. In this instance, such an approach might lead to treatments to slow or halt the growth of tumors or blood cancers that arose when B cells mutated and became malignant.