Study finds significant role of platelets in immune system

June 20, 2013

Scientists from the University of Calgary, Canada, have found through a study a new type of surveillance mechanism linked with immune system taking place in the liver of mice. It was noticed that platelets, which are conventionally known to play a significant role in the clotting of blood and are crucial to wound healing, while flowing across the blood stream in the liver of mice, were making frequent short-lived “touch-and-go” interactions with specialized immune cells called Kupffer cells. Kupffer cells are present in the liver and protect us from infection by capturing and eventually killing bacteria that pass by.

As per scientists, the touch-and-go mechanism was how platelets were scanning for captured bacteria. But when platelets detected a Kupffer cell bound to bacteria, the platelet-Kupffer cell interaction sustained much longer, which led to the killing of the bacteria.

How does it happen?

As per researchers, two receptor proteins on the surface of platelets — GpIb, and the GpIIb-GpIIIa complex have an affinity towards a protein (von Willebrand factor (vWF)) found on the surface of Kupffer cells. The GpIb receptor binds to the vWF long enough to scan for any captured bacteria. If they detect nothing, the platelet comes off and continues along the bloodstream in a touch-and-go interaction. However, when platelets found a Kupffer cell with captured bacteria the second receptor binds to the Kupffer cell resulting in a more prolonged interaction eventually leading up to the killing of the bacteria. Scientists are yet to examine the helpfulness of this binding in fighting infection.

This platelet-mediated surveillance mechanism has been shown to be vital for the mice because most (80-100%) mutant mice lacking platelets or GpIb receptors died within four hours of infection, whereas more than 90% of wild-type mice survived.

What about Humans?

Although the presence of same kind of mechanism in humans is yet to be confirmed, there is good evidence that human platelets can kill malaria infected red blood cells and in sepsis platelets appear to also be involved so they likely do play a role in immunity.

Efficacy of Aspirin questioned

The findings also question the efficacy of drugs like aspirin, which are known platelet inhibitors. If aspirin by its platelet-inhibitory role allows bacteria to survive longer in blood it could help bacteria become more resistant. There may be a need to reconsider aspirin use in immunosuppressed patients.

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