New HIV reservoir
Scientists have discovered another hidden "citadel" of HIV in the human body
Molecular biologists have discovered a third type of immune cells in which the immunodeficiency virus can hide indefinitely while trying to rid a person of infection, according to an article published in the journal Immunity.
"These cells, CTLA4, are found in many tissues of the body, including lymph nodes, spleen, intestines and bone marrow, and they can contain full-fledged viral particles. Accordingly, the fight against these cells will not only help reduce the number of potential sources of re–infection, but also help the immune system to fight HIV more strongly," said Mirko Paiardini from Emory University in Atlanta (USA).
As scientists explain, today HIV patients can live for decades thanks to the use of antiretroviral drugs – substances that suppress various stages of virus replication in the cells of the body. Since they often have strong side effects, doctors are often forced to stop taking them for several weeks.
When they stop taking them, HIV "gets out of the trenches" and begins to intensively copy itself, often returning to the initial scale of infection in three or two weeks. In recent years, scientists have been actively trying to find drugs or antibodies that would help avoid such a "counterattack" of the virus, or would allow the virus to be "kicked out" of cells.
Relatively recently, biologists have found out that the virus "digs in" not only in the T-cells that it usually infects, but also in the so–called macrophages - amoeboid cells that destroy bacteria, toxic particles and various "garbage". This discovery forced scientists to embark on a large-scale search for other "bunkers" of HIV in humans and animals.
Payardini and his colleagues discovered another such hidden reservoir of the virus by studying what happens to the body of several rhesus monkeys (Macaca mulatta) infected with VIO, the "monkey" version of HIV, and treated with antiretroviral drugs at the university clinic.
The drugs suppressed the reproduction of the virus in primate T-cells, but scientists suspected that the VIO particles could be hiding in other immune cells living in their lymph nodes and in other body tissues. To do this, scientists introduced a special substance into primate cell samples, attached to fragments of viral RNA or DNA, and made them glow, and conducted a "census" of those cells in which traces of VIO were found.
In addition to "ordinary" T cells and macrophages, scientists found that full-fledged particles of the immunodeficiency virus were hiding in another type of immune cells – in the so-called CTLA4 cells. They are a special kind of regulatory T-cells responsible for suppressing the immune response.
Having made this discovery, primatologists turned for help to colleagues from an Atlanta clinic who monitor the health of HIV-infected people. Doctors collected lymph samples from six volunteers and found traces of infected cells of the same type in them, which indicated that these same CTLA4 cells can contribute to the survival of the virus in patients' bodies when taking medications.
The discovery of three types of immune cells that HIV infects at once suggests that the process of completely getting rid of it will be extremely difficult. Scientists will have to create immunotherapy or some other drugs that will destroy HIV in all these cells without touching other parts of the immune system.
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