Dr. Gayle Baldwin, AIDS researcher at the University of California Los Angeles who led the study, said that the same phenomenon probably occurs in humans. But proving it would be difficult; she and others said such a study in humans would be unethical.
"Cocaine not only influences risky behaviors, it also has a direct and profound effect on the AIDS virus," said Baldwin.
The spread of the virus and its effects on immune cells known as CD4 T-cells are directly related to how sick a person becomes with HIV infection.
Baldwin knew that people who use drugs are more likely to become infected with HIV and she knew this was also the case specifically with cocaine, which is not usually injected -- the usual route of HIV infection for drug users.
"There were some studies done quite some time ago that suggested a correlation between cocaine use and the progression of disease in HIV-positive individuals," Baldwin said in a telephone interview.
"We found that cocaine can dramatically increase the spread of HIV infection in a mouse model," Baldwin said.
She also knew that cocaine can affect the immune system.
Writing in the online edition of the Journal of Infectious Diseases, Baldwin said she and colleagues tested specially bred mice that are infected with the human AIDS virus.
Half the mice got daily injections of liquid cocaine and half got salt water. They tested the mice 10 days later.
"We saw a 200-fold increase in AIDS viral load in the blood of the animals injected with cocaine compared to those that received the placebo," Baldwin said. "In only two weeks, the drug radically stimulated the production and spread of HIV."
Viral load is a measure of how much virus is circulating in the blood. Baldwin's team also looked to see how many CD4 cells had been killed.
"The cocaine increased HIV's efficiency so dramatically that it nearly wiped out the CD4 T-cells. We found nine times fewer CD4 T-cells in the cocaine-treated mice than in the animals that received the placebo," Baldwin said.
"This means that the cocaine produced a spectacular double outcome," she added. "Not only did the drug double the number of HIV-infected cells, it produced a nine-fold plunge in the number of T-cells that fight off the virus."
The cocaine could be working on many levels, Baldwin said.
It could be increasing the number of molecular doorways, called receptors, that HIV uses to get into the cells it infects. Cocaine may cause cells to sprout more CCR5 and CXCR4 receptors, both of which are used by HIV, she said.
It may also increase the levels of cytokines, chemical messengers, such as TGF-beta and IL-10, which also affect HIV.
A revved-up immune system only helps HIV, which is so insidious and difficult to fight because it thrives on and destroys the very cells sent to attack it.
Baldwin said her work could b important, because recent studies show that younger people are returning to risky sexual behavior, such as not using condoms, because they are losing their fear of AIDS.
"Cocaine is still a very bad problem in populations at risk," she said.
She said it is not clear whether taking cocaine might make a person more likely to contract HIV from an infected sex partner or a contaminated needle.
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