1- Haemostatic Mechanism3

➢During the release reaction, the contents of the granules are
discharged into the open canalicular system.
Platelet antigens
Several platelet surface proteins have been found to be important
antigens in platelet‐specific autoimmunity and they have been
termed human platelet antigens (HPA).
In most cases,two different alleles exist, termed a or b alleles (e.g.
HPA‐1a).Platelets also express ABO and human leucocyte antigen
(HLA) class I but not class II antigens.