The theory has been that the virus binds to several extracellular proteins--"gates" through which the disease must pass before entering the cells.

Until recently, only one of these proteins was known--the immune cell receptor CD4.

Last year, Associate Professor of Pathology Joseph G. Sodroski found two other gate proteins that HIV uses to enter cells in the rest of the body--CCR5 and CXCR4.

Gabuzda used this discovery to try to find out if any of these proteins allowed HIV into microglia. She found that CCR5, and another protein--CCR3--are part of the complex that is the brain's gate for HIV.

These molecules had been suspected of being able to channel HIV "but this had only been suggested in recombinant DNA experiments," says Gabuzda. "This is the first time CCR3 has been shown to be the doorway."

Since the publication of this research in the Feb. 13 issue of the journal Nature, companies are already exploring its potential for therapeutic use.

"It is known that people who are deficient in the CCR3 receptor show no known abnormality, and further that they are highly resistant to HIV infection," says Gabuzda.

These facts are raising hopes that a drug which blocks the receptor could inhibit HIV's infection of the brain.

'Theoritically even if HIV were eliminated totally by other drugs from the body, it could resurface from hiding in the brain.' --Dan H. Gabuzda, Associate Professor of Neurology, Dana-Farber Cancer Insititute