Scientists have long assumed that Ebola's infamously high mortality rate was due to an ability to knock out the body's immune system and cause certain white blood cells to self-destruct, among other effects.
However, new research published Monday in the journal PNAS suggests that the human immune system doesn't give up that easily when confronted with Ebola virus disease.
In tests performed on the four Ebola patients treated at Atlanta's Emory University Hospital, doctors discovered that each of the patients' immune systems had mounted a surprisingly strong counterattack.
"We found a striking activation of both B and T cells in all four patients," wrote lead study author Dr. Anita McElroy, an infectious disease researcher at Emory.
McElroy and her colleagues found that immature B cells, or plasmablasts, that were actively secreting antibody accounted for 50% of all B cells in infected individuals, compared with less than 1% in healthy individuals.
Likewise, the frequency of activated CD4 T cells -- white blood cells that help direct immune cell response -- ranged from 5% to 30% in the patients, compared with 1% to 2% in healthy individuals.
But the most profound response was in the patient's CD8 T cells, or "killer T cells," researchers said. At least half of them showed signs that they were activated for battle.
"Taken together, these results suggest that all four patients developed robust immune responses during the acute phase of Ebola virus infection, a finding that would not have been predicted based on our current assumptions about the highly immunosuppressive nature of Ebola virus," authors wrote.
All four patients recovered. Among them were aid workers Dr. Kent Brantly and Nancy Writebol, who both received doses of the experimental drug ZMapp.
Study authors noted that all four patients received a variety of experimental treatments and it remained unclear whether any of them impacted the course of the disease, or affected immune response.
McElroy and her colleagues said the patients presented researchers with a rare opportunity to study the body's cellular immune response when confronted with Ebola virus.
Up until now, researchers have had to rely on the use of animals or test-tube experiments to study the virus, which can behave very differently in humans.
Study authors said they hoped their research might aid in the development of an Ebola vaccine.