Science & technology
Fed by the hand that should bite it
A bacterium that tricks the immune system into nurturing it
The immune system has many weapons with which to counter hostile incomers.
But what works against one may not be effective against another.
An interloper can take advantage of this by misdirecting the system into thinking it is fighting an enemy that it is not.
This buys time for that interloper to become entrenched.
That is sneaky.
Sneakier still, though, is the approach just discovered by Ruslan Medzhitov of Yale University.
As he and his colleagues report in Immunity, they have found a bacterium that induces its host’s immune system to release compounds on which it can then feed.
Mammalian immune systems have two modes of attack.
Type-1 is used against bacteria and viruses; type-2 against multicellular parasites such as worms.
Some invading bacteria, however, provoke a type-2 response when type-1 would be appropriate.
Dr Medzhitov decided to take a closer look.
He and his colleagues studied the behaviour of Pseudomonas aeruginosa, a bacterium which causes stubborn infections in people with cystic fibrosis.
They suspected it was leading the body to mount an ineffective type-2 response against it and wanted to know how it was doing this.
To explore the matter, they grew laboratory cultures of the sorts of epithelial cells that line human airways and monitored their gene-expression profiles when exposed to LasB, a toxic enzyme produced by the bacterium.
They found that LasB activated signalling pathways which drove the epithelial cells to make a protein called amphiregulin.
This forms the basis of a thick mucus that excels at ensnaring parasitic worms.
It also recruits immune cells called eosinophils, which are adept at attacking multicellular parasites.