快猫短视频

DOCTORS may soon have a powerful new weapon against a superbug that causes
food poisoning, toxic shock and many hospital infections. Researchers in the US
have found a way to block the bacterium鈥檚 most devastating strategy for
attack.

One of the reasons why Staphylococcus aureus can be so dangerous is
that many strains release 鈥渟uperantigens鈥� that send our immune system into
overdrive. These bacterial toxins bind to receptors on two different cell
types鈥攖he antigen-presenting cells that label foreign invaders for
destruction, and the T cells that rally other immune cells to attack. The
complex of cells linked to the toxin triggers an uncontrolled immune reaction,
culminating in the body turning on itself.

So Goutam Gupta and his colleagues at Los Alamos National Laboratory in New
Mexico decided to try to stop the superantigen from binding to the cells by
creating a decoy molecule that blocks the toxin鈥檚 assault. First, they
identified the parts of the gene for the superantigen that enable the toxin to
bind to human cells. Then they linked those sequences together to make an
artificial gene, which they inserted into E. coli bacteria.

The E. coli then churned out the decoy protein for them. 鈥淭his was
really the intellectual tour de force,鈥� says James Baker, director of the
University of Michigan鈥檚 Center for Biologic Nanotechnology.

Tests on human blood show the decoy protein binds to the antigen-presenting
cells and T cells like the superantigen. But because the decoy complex is a
different shape, it shouldn鈥檛 trigger a runaway immune reaction. However, Baker
warns that it might trigger a different one. 鈥淚鈥檇 be surprised if the body
didn鈥檛 make antibodies to it,鈥� he says.

Gupta now plans to try the decoys on mice infected with S. aureus. The
problem, he says, will be getting the decoys to the right place in the body.

Gupta worked with the strain of S. aureus responsible for a quarter of all
food poisoning in the US. But he thinks the decoy will also work against
superantigens produced by other strains鈥攕uch as the hospital superbug
methicillin-resistant S. aureus, or MRSA鈥攂ecause these
superantigens target the same binding sites on human immune cells. And because
the decoy molecule targets human cells, not bacteria, bacteria shouldn鈥檛 be able
to develop resistance.

The method could also be used to make decoys for other pathogens that subvert
immunity, such as the biowarfare agent anthrax. Such decoys could be valuable,
says Bob Ulrich of the US Army Medical Research Institute at Fort Detrick,
Maryland. 鈥淲hen it comes to biodefence issues, if you only have one thing in
your pocket you鈥檙e very vulnerable.鈥�