London, May 10 (IANS): Household air pollution can cause weaknesses in the immune function of the lung even in healthy people, which can lead to higher rates of pneumonia, a new research has found.

"Our cell based research has shown that HAP (household air pollution) exposure goes hand in hand with a reduced immune capacity to deal with lung infection. Vulnerable groups such as women and children in low income countries are most likely to be affected," said Jamie Rylance, respiratory specialist at Aintree University Hospital in Britain.

Three billion people worldwide are exposed to HAP from the fuels they burn to cook, light and heat with at home. Frequently, charcoal, wood and food waste are burned and generate high concentrations of smoke particles.

This exposure is associated with increased risk of pneumonia, particularly in low and middle income countries where bacterial pneumonia is the biggest cause of infant mortality. This risk is well known, but the reasons are not.

The new research offers an explanation.

In the southeast African country Malawi, the research team examined healthy volunteers who had frequent exposure to HAP. Using a telescope test, the team took samples of the immune cells from the lung airways.

These "alveolar macrophages" are a major defence against infection and clean up the lung airways by ingesting inhaled particles and bacteria.

Macrophage cells produce toxins which kill the bacteria they have taken up in a process called oxidative burst.

The study measured the smoke particle content of the macrophage cells. More smoke exposure was associated with a weaker killing response.

The study was published in the American Journal of Respiratory Cell and Molecular Biology.