Skin is more prone to infection and cancer with age
Older people are more at risk of skin cancer and infection because their skin is unable to mobilise the immune system to defend itself, UK research suggests.
It contradicts previous thinking that defects in a type of immune cell called a T cell were responsible for waning immunity with age.
In fact, it is the inability of the skin to attract T cells to where they are needed that seems to be at fault.
The findings are published in the Journal of Experimental Medicine.
Study leader, Professor Arne Akbar from University College London, said reduced immunity in older people is well known, but why and how it happens is not.
A number of volunteers - one group of 40-year-olds and one group aged over 70 - were injected with an antigen to stimulate an immune response from T cells.
As expected, the immune response in the older group was much less than that in the younger volunteers.
But when the researchers looked at the T cells there was nothing wrong with them.
What had declined in the older group was the ability of the skin to attract T cells - effectively the signals to direct them to the right place were missing.
Further experiments with skin samples in a test tube showed that the skin was still able to send the appropriate signals when pushed, suggesting the problem is reversible.
"At the outset we thought it would be the cells responsible for combating infections that might be at fault, but the surprising thing was the T cells were fine but they couldn't get into the skin - the signals were missing," Mr Akbar said.
He said it raised the possibility of ways to boost the immune system in older people to give them a better chance of fighting infection and reducing the risk of skin cancer.
"The question that it raises is what survival advantage there is to this, is there a negative reason for having too much immunity in the skin when you get older?
"Going in to intervene may have consequences that we don't realise and that's where we need to do more research."
He added that the same immune problems may be apparent in other tissues in the body.
Steve Visscher, deputy executive at the Biotechnology and Biological Sciences Research Council, which funded the research, said knowing more about the ageing process was vital as people increasingly live longer.
"The more knowledge we have about healthy ageing, the better we get at preventing, managing and treating diseases that are simply a factor of an ageing body."