The deadly AIDS virus can infect bone marrow cells, which may then serve as a reservoir for infection of other cells in the body, AIDS researcher Dr. Anthony Fauci said Monday.

Fauci, head of the National Institute of Allergy and Infectious Diseases, also told a large medical conference that his research team has discovered a hormone produced naturally by the body in response to shock or infections that can switch on the AIDS virus.The hormone transforms a latent infection that causes no symptoms into an active killer disease.

Fauci said the bone marrow discovery "isn't any breakthrough, but it explains some of the puzzles of the (AIDS) virus."

For example, he said, the finding explains why some AIDS patients show blood abnormalities, and represents the first time anyone has shown the AIDS virus can enter cells lacking a special surface feature called the CD4 receptor once thought to be the virus's only gateway into human cells.