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See Inside June 2009

Yanking Pathogens Out of Blood with Magnets

Germ-grabbing magnetic beads that can be pulled from the blood

Using a magnetic field to literally pull diseases from the bloodstream sounds like a sci-fi dream. But scientists may have found a way to do just that, at least for sepsis, a potentially lethal blood infection that can lead to multiple-organ failure.

Biologist Donald E. Ingber of Harvard Medical School, his postdoctoral fellow Chong Wing Yung and their colleagues have devised a way to filter pathogens from the blood of septic patients using micron-size magnetic beads. In their model system, beads coated with an antibody that binds to sepsis-causing bacteria or fungi mix with blood drawn from a patient. After the antibody-coated magnets have bound with the pathogen, they are pulled via a magnetic field into a saline solution that flows alongside the blood and sweeps them away. The filtered blood goes back into the patient. In tests using 10 to 20 milliliters of blood, the method removed 80 percent of the pathogens.

A key reason for the successful filtration was the size of the beads, which are about one-eighth the diameter of red blood cells. They are small enough that the flow of saline solution remains smooth; turbulence would end up mixing the solution with the blood and make separation of the germs and blood more difficult.

Ingber thinks a more advanced version of his system, which he described in the May 7 Lab on a Chip, could solve a headache for intensive care units that must determine whether a sepsis case stems from a bacterium or a fungus. Because fungal medications can be toxic, they are ordinarily withheld until a diagnosis confirms the pathogen type. Such a diagnosis takes time, however, which could jeopardize a rapidly declining patient. Ingber hopes to incorporate different kinds of sticky proteins on the beads to pull out several types of microbes at once, without having to make a diagnosis.

He also thinks it is not necessary to remove all the germs. “What we’re trying to do is establish a tipping point,” Ingber says, referring to the amount of pathogens in the body. His theory is that lowering the number of bacteria or fungi will enable the antibiotics or fungicides to work more efficiently.

“It’s a very elegant, very new theory,” comments Tonse Raju, a neonatologist at Eunice Kennedy Shriver National Institute of Child Health and Human Development. “My hat’s off to them for thinking differently.” But, he notes, the theory has a major problem: namely, there is no proof yet that thinning the pathogen ranks will help medications work better. Besides, much of the damage from sepsis comes from the body’s own inflammatory response, not the germs. Another problem, Raju points out, is that some bacteria and fungi can hide in pus pockets or in areas of low blood supply such as the peritoneal cavity and thus could avoid the blood cleansing.

Still, Ingber remains undaunted. He has begun preliminary testing on rabbits, because they are about the size of premature infants, who have very high rates of sepsis. Ingber acknowledges the practical roadblocks ahead but hopes that with further study magnetic stripping of disease will not be just science fiction.

Note: This article was originally published with the title, "A Bead on Disease".

This article was originally published with the title "A Bead on Disease."

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