Pregnant women’s immune response to Flu goes up, not down

New research has found that influenza causes a surprisingly strong reaction in the usually more placid immune systems of pregnant women. The finding could lead to new treatments for pregnant women with sever influenza. Immunologically speaking, the developing foetus is a foreign object to a mother’s immune system.

So to prevent rejection of the foetus their immune systems are usually reigned in somewhat, even at the risk of being more open to infections. Flu seems to be particularly risky for pregnant women, and is more likely to lead to pneumonia and severe complications.

During the 2009 swine flu (H1N1) pandemic, infected pregnant women in Australia and New Zealand were 13 times more likely to be admitted to hospital with a serious illness than non-pregnant women. The researchers in this study took natural killer (NK) cells and T-cells – both important in fighting viral infections – from pregnant and non-pregnant women before and after a seasonal flu vaccination.

They then exposed the cells to pandemic ‘swine flu’ (H1N1) and seasonal (H3N2) influenza viruses and measured their responses, compared to a general stimulatory cocktail (PMA/Ionomycin). They found that while the dampened immune response was present with the stimulatory cocktail compared to non-pregnant women, pregnancy actually enhanced the responses of these cells. NK and T-cells from pregnant women produced greater levels of cytokines and chemokines, such as IFN-γ and MIP-1α.

This is a surprising result, considering that pregnant women’s immune systems are considered to be dampened. The researchers think this provides evidence for influenza being a hyper-inflammatory disease rather than a state of immune deficiency. As such, dampening the heightened immune system in pregnant women severely infected with influenza could be a new treatment option.

However, before this new treatment path can be trodden there needs to be more work to confirm the findings in acute influenza infection and to confirm if the increased chemokine and cytokine production contribute the higher susceptibility of pregnant women to severe pneumonia and other complications.

Source: Kay, a. W., Fukuyama, J., Aziz, N., et al (2014). Enhanced natural killer-cell and T-cell responses to influenza A virus during pregnancy. Proceedings of the National Academy of Sciences, 1–6. DOI:10.1073/pnas.1416569111

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