IMMUNOCYTOCHEMICAL LOCALIZATION OF THE CHEMOKINES RANTES AND MIP-1-ALPHA WITHIN HUMAN PLATELETS AND THEIR RELEASE DURING STORAGE

The cytokines RANTES and MIP-1 alpha are 8-kD peptides which belong to the C-C subfamily of chemokines. They are both potent chemotactic fac tors for basophils and eosinophils. Apart from lymphocytes, the RANTES peptides was recently shown to be released from human platelets stimu lated with thrombin [Kameyoshi et al: J Exp Med 1992;176:587-592]. Emp loying postembedding immunocytochemistry, we could detect RANTES and f or the first time also MIP-1 alpha within the a-granules of human plat elets. To date, MIP-1 alpha was not reported to occur in platelets. In slightly activated platelets, as found in stored platelet concentrate s (PC), label for RANTES and MIP-1 alpha. could also be observed withi n cisterns of the open canalicular system and on the plasma membrane, indicating a release of both peptides. These findings were confirmed b y in vitro studies in PC, by investigation of RANTES and MIP-1 alpha r elease into the suspending medium. Over a period of 8 days, RANTES was steadily released in relatively high amounts, whereas MIP-1 alpha was measured in rather small amounts in the suspending medium. As RANTES and MIP-1 alpha, besides their chemotactic activity on eosinophils and basophils, are able to mediate the release of histamine, it is tempti ng to speculate about a participation of platelets in inflammatory rea ctions in which eosinophils and basophils are involved.