Immune response turned up, not down, by flu during pregnancy, study finds

September 22, 2014
influenza
Electron microscopy of influenza virus. Credit: CDC

Pregnant women have an unusually strong immune response to influenza, an unexpected finding that may explain why they get sicker from the flu than other healthy adults, new research from the Stanford University School of Medicine and Lucile Packard Children's Hospital Stanford has found.

The results were surprising because immune responses are thought to be weakened by pregnancy to prevent the woman's body from rejecting her fetus.

The study, which will be published online Sept. 22 in the Proceedings of the National Academy of Sciences, is the first to examine the reactions of immune cells taken from to viruses, including the H1N1 strain that caused the 2009 pandemic.

"We were surprised by the overall finding," said Catherine Blish, MD, PhD, assistant professor of and the study's senior author. "We now understand that severe influenza in pregnancy is a hyperinflammatory disease rather than a state of immunodeficiency. This means that treatment of flu in pregnancy might have more to do with modulating the than worrying about viral replication."

In the study, immune cells taken from 21 pregnant women and 29 healthy, nonpregnant women were exposed to different flu viruses in the lab. The immune cells were obtained by collecting blood samples from the women before and seven days after they received flu vaccines. Cells taken from pregnant women six weeks after their babies were delivered were also tested. The researchers studied responses to two flu viruses: pandemic H1N1 and a strain of seasonal influenza, H3N2.

Pregnancy enhanced the immune response to H1N1 of two types of : natural killer and T cells. Compared with the same cells from nonpregnant women, H1N1 caused pregnant women's NK and T cells to produce more cytokines and chemokines, molecules that help attract other immune cells to the site of an infection.

"If the chemokine levels are too high, that can bring in too many immune cells," Blish said. "That's a bad thing in a lung where you need air space." Getting the flu during pregnancy, especially pandemic strains such as those that caused the pandemics of 1918, 1957 and 2009, carries a heightened risk for pneumonia and death, she noted.

Both strains of flu also caused NK and T cells to be activated in a greater variety of ways in pregnant than nonpregnant women, the study found.

Today, pregnant women with influenza are usually treated with drugs to slow the replication of the flu virus in their bodies. Although this is a useful treatment, the new findings suggest that it isn't the only good option, the study's authors said.

"If our finding ends up bearing out in future studies, it opens the possibility that we can develop new immune-modulating treatment approaches in the setting of severe influenza, especially in pregnant women," said Alexander Kay, MD, instructor in pediatric infectious diseases and the study's lead author.

The researchers are curious about whether the response of pregnant women's to other viruses would be similarly heightened, an idea they have yet to test.

"I suspect this is peculiar to influenza for a variety of reasons," Blish said. Having influenza during pregnancy quadruples a woman's risk for delivering her baby prematurely, she said.

"I wonder if this is an inflammatory pathway that is normally activated later in pregnancy to prepare the body for birth, but that flu happens to overlap with the pathway and aberrantly activates it too early," Blish said.

Blish and Kay plan to continue the research by studying pregnant and nonpregnant women who have contracted flu infections in their day-to-day lives.

And they hope that their research will remind women who are pregnant or planning a pregnancy to get their flu shots. "Flu vaccination is very important to avoid this inflammatory response we're seeing," Kay said. "But only 50 percent of pregnant women are currently vaccinated for influenza."

Explore further: All pregnant women need flu shot: Ob/Gyn group

More information: Enhanced natural killer-cell and T-cell responses to influenza A virus during pregnancy, Proceedings of the National Academy of Sciences: www.pnas.org/cgi/doi/10.1073/pnas.1416569111

Related Stories

All pregnant women need flu shot: Ob/Gyn group

August 19, 2014
(HealthDay)—A group representing U.S. obstetricians is calling for all pregnant women to get a flu shot.

Flu vaccine for expectant moms a top priority

September 18, 2014
Only about half of all pregnant women in the U.S. get a flu shot each season, leaving thousands of moms-to-be and their babies at increased risk of serious illness.

Why aren't pregnant women getting flu vaccine?

August 18, 2014
Both mother and fetus are at increased risk for complications of flu infection during pregnancy. And prenatal care providers say they're advising women to get the flu vaccine, in line with recommendations from various organizations. ...

Study shows reduced risk of preterm birth for pregnant women vaccinated during pandemic flu

February 19, 2013
(Medical Xpress)—Pregnant women who received the H1N1 influenza vaccine during the 2009 pandemic were less likely to have premature babies, and their babies weighed more on average.

Flu vaccine protects mothers, babies

September 4, 2014
A study showing that the influenza vaccination of pregnant HIV-uninfected and HIV-infected women is safe and protects the women against confirmed influenza illness, has been published by researchers from Wits University and ...

Large study confirms H1N1 flu shots safe for pregnant women

January 16, 2013
Norwegian pregnant women who received a vaccine against the 2009 H1N1 influenza virus showed no increased risk of pregnancy loss, while pregnant women who experienced influenza during pregnancy had an increased risk of miscarriages ...

Recommended for you

Australian researchers in peanut allergy breakthrough

August 17, 2017
Australian researchers have reported a major breakthrough in the relief of deadly peanut allergy with the discovery of a long-lasting treatment they say offers hope that a cure will soon be possible.

Genetic variants found to play key role in human immune system

August 16, 2017
It is widely recognized that people respond differently to infections. This can partially be explained by genetics, shows a new study published today in Nature Communications by an international collaboration of researchers ...

Study identifies a new way to prevent a deadly fungal infection spreading to the brain

August 16, 2017
Research led by the University of Birmingham has discovered a way to stop a deadly fungus from 'hijacking' the body's immune system and spreading to the brain.

Biophysics explains how immune cells kill bacteria

August 16, 2017
(Tokyo, August 16) A new data analysis technique, moving subtrajectory analysis, designed by researchers at Tokyo Institute of Technology, defines the dynamics and kinetics of key molecules in the immune response to an infection. ...

How a nutrient, glutamine, can control gene programs in cells

August 15, 2017
The 200 different types of cells in the body all start with the same DNA genome. To differentiate into families of bone cells, muscle cells, blood cells, neurons and the rest, differing gene programs have to be turned on ...

Scientists identify gene that controls immune response to chronic viral infections

August 15, 2017
For nearly 20 years, Tatyana Golovkina, PhD, a microbiologist, geneticist and immunologist at the University of Chicago, has been working on a particularly thorny problem: Why are some people and animals able to fend off ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.