Aspirin may thwart the defensive role of these blood cells against malaria.

Platelets are one of the body's interim defenses against malaria

In the developing world, treating malaria usually involves anti-malarials to kill the parasite and aspirin to control the fever. But according to new research, aspirin may hamper the body's ability to fight malaria. The study found that blood platelets can kill malaria parasites—in the genus Plasmodium—but lose that ability if exposed to aspirin.

Plasmodium parasites infect red blood cells and have highly variable surfaces, making each infection a new challenge for the body, says HHMI international research scholar Simon Foote of the Menzies Research Institute at the University of Tasmania. “It takes quite a bit of time to develop a specific immune response to protect you from malaria. During that time, the body somehow has to stop you from dying.”

In the February 6, 2009, issue of Science, Foote and his colleagues report that blood platelets—involved in blood clotting—might be one of the body's interim defenses. The group discovered that mice genetically engineered to produce fewer platelets than normal were far more likely to die from a rodent version of malaria than other mice.

To determine whether low platelet levels directly caused this effect, the team gave aspirin, known to inhibit platelet function, to a group of mice lacking the mutation. Like the genetic mutants, the aspirin-fed subjects were more susceptible to the disease.

Foote and his team also exposed Plasmodium-infected human red blood cells to platelets. As they watched, the platelets bound to the cells and killed the parasites—an ability they lost when aspirin was added.

It's been known that platelets bind preferentially to malaria-infected red blood cells, says Foote. Researchers had hypothesized, however, that these cell-bound platelets posed a danger to the infected body—they can build up in small blood vessels and cause clots in the brain. “They're essentially the glue between infected cells and vessels...and they promote blockage,” he says. The new study suggests that platelets may do some good as well.

According to Foote, it's unclear how platelets' Plasmodium-killing ability functions, and the laboratory results don't necessarily translate to infected humans. “I think this needs a really good, closely monitored clinical trial,” he says.

Photo: Scimat / Photo Researchers, Inc.