HIV can be harbored in brain cells and, from there, use white blood cells to ship the infection to other organs in the body, as shown by a new study from the US National Institutes of Health (NIH).
The study, reported in the journal PLOS Pathogens, specifically looks at a type of brain cell known as astrocytes, spindly star-shaped glial cells that can be found in their billions across the brain and spinal cord. Scientists from the NIH and Rush University Medical Center transplanted HIV-infected human astrocyte brain cells into the brains of immunodeficient mice to observe how it spread through the body's cells and organs.
HIV is a virus that infects CD4 cells, T cells (a type of white blood cell) that are a vital force for fighting off infection in the body. If left untreated, the virus can weaken a person's immune system and leave them unable to fight everyday infections, eventually resulting in a condition called AIDS (acquired immune deficiency syndrome).
In this new study, the researchers observed how the T cells, once infected from certain astrocytes, migrated out of the brain and into the rest of the body, trafficking the infection to organs such as the spleen and lymph nodes.
“This study demonstrates the critical role of the brain as a reservoir of HIV that is capable of re-infecting the peripheral organs with the virus,” said Dr Jeymohan Joseph, chief of the HIV Neuropathogenesis, Genetics, and Therapeutics Branch at NIH’s National Institute of Mental Health, in a statement.
“Our study demonstrates that HIV in the brain is not trapped in the brain — it can and does move back into peripheral organs through leukocyte trafficking,” added Lena Al-Harthi, PhD, lead study author at Rush University Medical Center.
It’s known that HIV can reside in the brain within days of the infection, but this new research importantly shows how brain cells can harbor the infection and resend it elsewhere in the body. This traveling HIV was even seen in the mice that were given combination antiretroviral therapy (cART), a widely used treatment for people with HIV that is taken daily, that suppresses the virus.
cART is not a "cure" for HIV, but it allows people with the infection to live relatively long and healthy lives by reducing concentrations of the virus in the body. This new research certainly doesn’t mean cART is ineffective, but it does indicate that the virus from the brain could roll into a full-blown infection if the treatment was stopped.
To follow up on their findings, the team studied donated brains of four deceased people with HIV who received effective cART treatment. They discovered some of the brains’ astrocytes contained traces of HIV DNA, suggesting the virus had resided here while receiving cART.
“The findings suggest that in order to eradicate HIV from the body, cure strategies must address the role of the central nervous system,” Joseph said.
"It also shed light on the role of astrocytes in supporting HIV replication in the brain — even under cART therapy,” added Al-Harthi.
Further research, as ever, is needed before scientists can reach more solid conclusions — after all, this has only been observed in a mouse model so far — but the study highlights how the nervous system plays a surprisingly important role in the spread of HIV throughout the body.