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 factors for basophils and eosinophils. Apart from lymphocytes, the RANTES peptides was recently shown to be released from human platelets stimulated with thrombin [Kameyoshi et al: J Exp Med 1992;176:587-592]. Employing postembedding immunocytochemistry, we could detect RANTES and for the first time also MIP-1 alpha within the a-granules of human platelets. To date, MIP-1 alpha was not reported to occur in platelets. In slightly activated platelets, as found in stored platelet concentrates (PC), label for RANTES and MIP-1 alpha. could also be observed within cisterns of the open canalicular system and on the plasma membrane, indicating a release of both peptides. These findings were confirmed by in vitro studies in PC, by investigation of RANTES and MIP-1 alpha release 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 tempting to speculate about a participation of platelets in inflammatory reactions in which eosinophils and basophils are involved.