Borrowed Time: The Science of How and Why We Age

by Sue Armstrong

In older people neutrophils are not as efficient at swallowing and killing – nor at casting their DNA nets – as they are in the young. But as we saw briefly in Chapter 4, one of the biggest problems with these immune cells is that they lose their sense of direction. When responding to a pro-inflammatory signal, elderly neutrophils zigzag through the tissue towards the site of injury like an emergency crew with a faulty GPS, causing collateral damage as they go. Looking at migratory patterns of neutrophils and their impact on tissues, Lord's team in Birmingham have found that ‘even in healthy elders, the amount of damage caused by neutrophils just wandering around the body looking for infections is double that in a young person’. So when in life does this become a problem? ‘We can pick it up in most 40- and 50-year-olds,’ says Lord. ‘But by the time you're 60 or 70 years old it's really bad. You struggle to find a neutrophil that is moving in the right direction efficiently.’ Blundering neutrophils are slow to reach their target, which is one reason why wounds heal so much more slowly as we age than they did when we were kids scuffing knees and elbows in the playground and quickly forming scabs. And they're one reason, too, why old people respond so poorly to infection. In severe infections such as pneumonia, old people's neutrophils are even more disorientated than usual, and the collateral damage they do in migrating to the site is vastly increased – up to five times high...