Immunity mechanism discovered

Platelets, a component of blood typically associated with clotting, were discovered to actively search for specific bacteria, and upon detection, seal it off from the rest of the body. The findings, which were published in Nature Immunology this week, provide the science community with a greater understanding of immunity.

“The science community has known that platelets do participate in immunity, but now it's been demonstrated that they have a way of actively searching for bacteria,” says Craig Jenne, PhD, one of the authors of the study and a member of the university's Snyder Institute for Chronic Diseases.

The vast majority of bacteria in the blood stream is trapped by the liver in a network of specialized cells known as Kupffer cells. Once trapped, a series of immune processes take place to eradicate the bacteria; however, this can take several hours, lending time to harmful bacteria to multiply and release toxins into the neighboring cells, subsequently causing infection and cell damage and death.
“Upon entering the blood stream, bacteria can start to divide within several minutes,” he says. “So if you're waiting for the immune system to deal with it, the bacteria could become an infection before it gets there.”

Through imaging of the liver in animal models, scientists discovered that platelets are constantly interacting with the Kupffer cells by 'touching' them to search for captured bacteria. If nothing is detected, or if the bacteria isn't deemed particularly harmful, the platelets will move on; however, if harmful bacteria is detected, the platelets will bind to it, sealing it off from the body until the immune system can rid the bacteria altogether. This happens within seconds of cell capture and thus reduces the likelihood of infection.

“If this instantaneous response didn't exist, it could be a matter of life and death,” he says.

Interestingly, it was observed that while this touch-and-go mechanism is happening continuously, platelets only appear to create this barrier around particularly harmful bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MRSA can lead to serious and potential fatal conditions such as sepsis, and is spread through skin to skin contact.

“We now have a completely different angle of how the immune system deals with specific types of bacteria,” says study author Paul Kubes, PhD, who is also director of the Snyder Institute for Chronic Diseases. “Going forth we can begin to look at how we can help our own defenses deal with these types of bacteria.”

To watch two different videos of the mechanism visit: http://www.youtube.com/watch?v=cUpIkSXoQUY (platelets searching for bacteria)

http://www.youtube.com/watch?v=vcGOQpzTlT0 (platelets encapsulating pathogens)