Pregnant women may be more vulnerable to swine flu because an infection-fighting blood cell fails to do its job within this group, Australian doctors said.
The finding emerged after doctors in Melbourne analyzed blood tests to determine why pregnant women made up a majority of their critically ill H1N1 patients. The results, reported at a medical meeting in San Francisco, showed six out of seven of the women lacked a cell known as immunoglobulin G subclass 2, or IgG2. The antibody deficiency was also noted in seriously ill non-pregnant patients.
Doctors are now looking for the defect in others with the virus to confirm the association and determine whether it can help identify patients at risk of pneumonia and other complications. The hospitalization rate for pregnant H1N1 patients is more than four times that of the general population, a study last month in the medical journal Lancet found.
“This is the first time IgG2 subclass deficiency has been associated with influenza,” Claire Gordon, an infectious diseases doctor at Melbourne’s Austin Hospital and the study’s lead author, told the Interscience Conference on Antimicrobial Agents and Chemotherapy.
Gordon said she and her colleagues suspect the deficiency is linked with an inability to mount a rapid response to the flu infection, leading to severe disease. IgG2 antibodies help eradicate bacteria, and studies in mice have shown them to fight influenza and viral infections in the lungs, she said.
The investigation was prompted by a 28-year-old pregnant H1N1 patient who developed such severe breathing difficulties that she required her blood to be pumped through an artificial lung, a life-supporting procedure known as extracorporeal membrane oxygenation, or ECMO, Gordon said. Doctors questioned whether the patient’s complications were caused by an underlying immune disorder.
“Somewhat unexpectedly, we identified the IgG subclass deficiency,” Gordon said.
Blood tests on 16 healthy pregnant women used in the study for comparison found more than half were “mildly deficient” in an immunoglobulin G subclass, she said. The lowest IgG2 levels were recorded in the severely ill pregnant swine flu patients.
“The fact that pregnancy appears to be associated with mild IgG2 deficiency may explain their increased risk,” the authors said. “But severe cases are significantly more deficient.”
More research is needed to assess whether severely ill patients with the deficiency would benefit from immunoglobulin treatment, Gordon said.
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