Emory, CDC find immune response to Ebola virus

By Holly Korschun

A group of scientists from Emory and the Centers for Disease Control and Prevention (CDC) has discovered that a mouse strain of Ebola virus adapted from a human strain, induces a strong T-cell immune response despite some scientists’ belief that the lethal effects of Ebola are due to a virus-caused suppression of the immune system.

The new information about the immune response to Ebola could be an important step in developing an effective vaccine against the disease.

Ebola is an RNA virus that causes a severe hemorrhagic fever in humans and non-human primates, beginning within a few days of infection, with mortality of 50 to 80 percent in as little as one week.

The mouse-adapted strain tested by the Emory and CDC scientists produces 100 percent mortality in mice within six-to-eight days following injection of a low dose of virus.

Using markers of T-cell activation, the scientists detected a high frequency of activated T-cells in mice beginning as early as four days after infection. In addition, they detected high levels of the cytokine interferon gamma in the spleen, liver and serum. Cytokines are proteins produced by T-cells that prevent the growth of viruses and make cells resistant to viral infection.

The researchers concluded that despite the measurable immune response, Ebola causes its severe and rapidly fatal response in mice because the virus is so lethal that it allows no time for the immune T-cells to multiply and mount an attack. The research was conducted by Manisha Gupta, a postdoctoral fellow in immunology at Emory and CDC; Rafi Ahmed, professor of microbiology and immunology and director of the Vaccine Research Center; and CDC scientists Siddhartha Mahanty and Pierre Rollin.

In additional experiments, the scientists removed all of a certain kind of T-cell from a subset of mice and did not detect interferon gamma, suggesting that the T-cells are the major source of cytokines induced by Ebola during acute infection.

Further, scientists have shown that memory T-cells, in the absence of anti-Ebola antibodies, can protect against lethal infection.

In ongoing research, the scientists are working to understand the mechanism of immune protection, which will help in the design of an Ebola vaccine.