Red blood cells (RBCs) take on a new shape and perform important functions in contracted blood clots, a new study suggests.
Researchers found that, during clot contraction, RBCs can be compressed into many-sided, closely packed, polyhedral structures.
These polyhedral RBCs form an impermeable seal within the clot to stem bleeding and help prevent vascular obstruction. And the cells may be the reason fibrinolysis is hampered after clot contraction.
John Weisel, PhD, of the University of Pennsylvania in Philadelphia, and his colleagues described these findings in Blood.
The researchers knew that, after a blood clot forms, the actin and myosin in platelets start the contraction process and cause the clot to shrink to about one-third of its original size. RBCs are caught up in the contraction process and get pulled by platelets toward the interior of the clot.
But little was known about the structure of contracted clots or the role RBCs play in the contraction process. So Dr Weisel and his colleagues decided to study clot contraction using a novel magnetic resonance technology.
“We found that contracted blood clots develop a remarkable structure, with a meshwork of fibrin and platelet aggregates on the exterior of the clot and a close-packed, tessellated array of compressed polyhedral erythrocytes within,” Dr Weisel said.
The team saw the same morphology in clots created from human blood reconstituted with its cellular and plasma components, as well as clots made with mouse blood.
The polyhedral erythrocytes, or polyhedrocytes as the researchers named them, were also present in human arterial thrombi taken from patients with myocardial infarctions.
The researchers believe the RBCs take on the polyhedral shape so as to decrease volume, surface energy, or bending energy.
The team said their findings might have clinical implications. It is well known that, with time, thrombi develop resistance to being broken up by thrombolytic agents.
And the nearly impermeable barrier formed by RBCs within the contracted clots may help to explain why. Clot contraction could be a target of intervention to prevent the formation of the closely packed polyhedrocytes.
