Babies respond to mum's flu jab
Fetal immune system not so naive after all.
When a pregnant mother receives her recommended flu vaccine, she's not the only one whose immune system gears up to battle the virus. Her fetus can also mount an immune response against the flu, say researchers in the United States.
The finding runs contrary to the stereotypical view of the fetal immune system. For more than 50 years, this has been thought of as at best wimpy, capable of some basic, general responses but not the elegant, finely targeted defences found in adults.
But allergy researcher Rachel Miller of Columbia University, New York, and her colleagues found that about a third of babies born of vaccinated mothers were equipped with cells tailor-made to fight off the flu virus.
"This indicates that the baby's got a pretty well-developed immune system by the time it's born," says immunologist William Burlingham of the University of Wisconsin-Madison.
Whether the immune cells are enough to ward off infection from the virus has not been tested. But their existence shows that the neonatal immune system can make immune cells to fight specific antigens.
The findings could have important public health consequences if the babies do become resistant to flu, says Ofer Levy, a physician and immunologist at Harvard Medical School. "This raises the possibility that if you optimize vaccines, you might be able to protect both the mother and the newborn," he says.
Some researchers believe that exposure in the womb to antigens from, for example, specific foods or cigarette smoke can affect the development of later allergies. But Miller urges caution before extrapolating from her results to other antigens.
"This was a very strong stimulant," says Miller of the vaccination. "We don't know how generalizable that will be."
Fetuses fight back
The fetal immune system was thought puny because newborn babies are highly susceptible to infection. And they have few of the immune cells involved in recognizing specific antigens. Also, says Burlingham, researchers often study the question in mice, which have a less developed immune system at birth than humans.
Recently, there has been some evidence that the neonatal immune system is more sophisticated than once thought. But it is difficult to detect T cells targeted against a specific antigen, and previous work used techniques that were criticized for their lack of specificity.
To home in on the baby's immune system, Miller used a fluorescent molecule that mimics the antigen, and lights up when the appropriate immune cell sticks to it.
The researchers screened umbilical-cord blood from babies born to women who'd been vaccinated against the flu during their second or third trimester. They found that about one in three babies had produced antibodies and T cells designed to attack the flu virus.
The cells contained protein sequences encoded by DNA inherited from dad, ruling out the possibility that the cells were acquired direct from mum. The results are published today in the Journal of Clinical Investigation1.
"This says that the antigens introduced to the mother through vaccination are transferred to baby, and the baby's immune system is responding," says Burlingham. "There's the potential here that these babies could have some useful immunity." Burlingham says that his lab has achieved similar results using other antigens.
- Rastogi D., et al. J. Clin. Invest., 117 . 1637 - 1646 (2007).