Novel aspects of platelet factor XIII function

Pools of factor XIII (FXIII) exist in the plasma and within the cytoplasm of hematopoietic cells, including platelets. The functions of the cellular form, FXIII-A, have been assumed to be intracellular in nature, as the protein lacks a signal sequence for its release. Mounting evidence now suggests that platelet FXIII-A modulates hemostasis by several different mechanisms. In this condensed review we discuss recent advances in our understanding of the novel intracellular and extracellular functions of platelet FXIII-A.