Kids need to eat dirt to be immune

A dose of dirt might be what the doctor ordered for a healthy immune system, new research has shown.

Stanford immunologist Mark Davis, who led the study which is published this week in the journal Immunity, compared the spectrum of immune cells contained in blood samples from adult donors and new-born babies.

Focusing on a subset of white cells called CD4 lymphocytes, which orchestrate the immune response by recognising pathogens and stimulating other cells to attack, Davis and his team found that, in the adults, there were CD4 cells capable of recognising all of the pathogens they tested.

Furthermore, up to 90% of the CD4 cells were memory cells; that is, quick-reacting cells that are made when an individual has met a particular threat previously.

The samples from the babies showed that they too had cells capable of recognising the pathogens, but, as one might expect, none of these cells were memory cells.

On it's own, this result doesn't sound surprising, until one realises that the adult donors had not actually ever been infected with some of the pathogens - such as HIV - being tested by the team.

So where were these memory cells coming from in the adults? "We don't know for sure," says Davis.

But he speculates that infections with low-virulence bugs trigger the immune system to develop also responses to other related bugs it hasn't seen before.

"We think this happens by about age ten," he says. "Now we need to work out how to prove it," because obtaining blood samples in this age group is tricky.

Davis likens the development of the immune system to the maturation of the brain.

"The brain needs to have input from the eyes for the visual system in order to see properly. The immune system's no different. It needs stimulating in childhood to make it develop properly."

Moreover, the findings might also explain why young children are much more vulnerable to infections that adults tend to brush aside. The difference, of course, being that, in adults, these immune memory responses discovered by Davis will have matured, so the adult immune response is far more robust and effective.

"Kids need to eat dirt!" says Davis, stirring his morning coffee, hopefully with a dirty spoon...