I have often suspected it, but we now have fresh evidence that blood platelets have a role in the immune system as well as in thrombosis.
Freom the New Scientist:
When bacteria enter blood they rapidly become coated in platelets, says Dirk Busch at the University of Munich in Germany. These sticky cell fragments then direct bacteria to the spleen, where they are engulfed by dendritic cells – immune cells that trigger a full-blown immune response.
This process relies on the interaction between a platelet receptor called GPIb and a blood protein called C3, which sticks to bacteria. When mice bred to lack C3 were injected with Listeria monocytogenes, platelets failed to surround the bacteria. Instead, they were destroyed by a different immune cell, the macrophage.
Although the macrophages cleared the bacteria, the lack of C3 prevented the formation of immunological memory – which enables the immune system to remember foreign invaders and respond to a future attack. Ultimately, Busch says it might be possible to boost platelet response to improve vaccines.