Natural killer, or NK cells, are part of our innate immune system. A healthy body produces them to respond early during infection. They are activated and they kill cells infected with a given virus.

It turns out NK cells are even more important to the body than previously thought. Researchers from Brown University and McGill University now know that the cells also help keep T cells - major players in cell-mediated immunity - from over-responding. Such a balance helps T cells maintain their role in the body’s adaptive immune response, rather than becoming too numerous and activated to cause harm.

The discovery, published in the September issue of The Journal of Experimental Medicine, could someday be used to help treat patients with compromised immune systems. Managing NK cell production might help stabilize the immune systems of people with HIV or keep patients from rejecting bone marrow or organ transplants.

The findings place an importance on understanding how to keep NK cells around, because they can be lost, said lead author Christine Biron, professor of medical science at Brown University.

“The work reveals two important aspects of NK cell biology, the first piece being understanding how to keep NK cells instead of losing them,” said Biron, the Esther Elizabeth Brintzenhoff Professor in the Department of Molecular Biology, Cell Biology and Biochemistry. “The second is that if you can keep them around, they have an important regulatory function to limit adaptive immune response. If you don’t have them during long challenges, your adaptive immune system response could go unregulated and lead to death.”

Scientists have known that NK cells have antimicrobial effects. But the newer research focuses on factors that help keep NK cells around. Through studying mice, researchers determined that the ability to keep NK cells around depends on whether they have a particular kind of activating receptor that promotes their proliferations.

Once activated, the expanded NK cells help produce a cytokine known as interleukin-10, which effects immunoregulation and inflammation control. (Cytokines are protein molecules that help regulate the immune system) In turn, IL-10 helps dampen the T cell response. An overabundance of T cells in this case can harm the body and cause death.

Biron said it was important to learn that it is possible to help make NK cells proliferate, as an important milestone to help sustain them in the body when needed.

Such an understanding is crucial, she said, to help patients with compromised immune systems who may not be able to sustain NK cells on their own.

Biron said the research underscores the need for balance in the immune system, with the right combination of NK and T cells to complement innate and adaptive immunity in the body.

“You want the right balance,” she said. “This could help create the right balance.”

The National Institutes of Health and the Canadian Health Institute funded the study.

Source:
Mark Hollmer

Brown University

The number of HIV-positive pregnant women taking antiretroviral drugs to prevent mother-to-child transmission increased in parts of Africa in 2008 to more than 50% of those in need of the medications, according to the United Nations’ 2009 progress report on HIV/AIDS, the Boston Globe reports. The report found that the number of people tested for HIV more than doubled in many countries in 2008, contributing to an increase in detection and the number of people taking antiretroviral drugs in the developing world.

U.N. said in its report that more than four million people worldwide are taking medication for HIV/AIDS. Mark Stirling, U.N.’s regional director for HIV/AIDS in Africa, said there was a “huge ramping up of AIDS services” between 2007 and 2008. He added, “It’s unprecedented. In the acceleration and intensification of reach, 2008 was an extraordinary year” (Dugger, Boston Globe, 10/1).

Teguest Guerma, the interim HIV/AIDS director for the World Health Organization, said the “greatest gains” were in sub-Saharan Africa, which accounts for two-thirds of HIV cases. According to Guerma, about 2.9 million people in the area were receiving treatment for HIV/AIDS by the end of 2008 (Wilson, “All Things Considered,” NPR, 9/30). According to the Globe, a large-scale international effort to fight AIDS — financed by the U.S., European countries and other donors — helped ensure that more African children with HIV received antiretroviral drugs. The number of children taking the medications rose from 198,000 in 2007 to 275,700 in 2008.

The report also found that 2.7 million new cases of HIV occurred in 2007, the most recent year for which estimates are available. Many African countries in 2008 began the framework for programs to broadly offer male circumcisions, which can lower the risk of HIV, the report noted. However, leaders need to be more outspoken about the benefits of circumcision and about how having multiple long-term sexual partners contributes to the epidemic, according to the report (Boston Globe, 10/1).

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