A controversial discussion as to whether human platelets are capable of regulated protein synthesis has been ongoing for over half a century. A previous study has suggested that human platelets synthesize large amounts of interleukin 1beta (IL-1beta) in response to external cues and in a physiologically significant manner. However, cytokines such as IL-1beta are generally considered to be products of leukocytes and it could not be completely excluded that contaminating leukocytes may have contributed to the IL-1beta results in platelet preparations. It was therefore our intention to investigate whether residual leukocytes had an impact on thrombin-induced IL-1beta synthesis. Using various methods to reduce the level of contaminating leukocytes, we found that IL-1beta production in platelet-rich suspensions is dependent on the presence of leukocytes, as it was decreased by reducing the number of leukocytes. In addition, we found that thrombin-induced IL-1beta synthesis was completely eliminated in leukocyte-free platelet preparations and could be restored by adding leukocytes. IL-1beta synthesis could be detected in platelet suspensions contaminated with at least 1 leukocyte per 10(5) platelets. This study demonstrated that platelets are incapable of synthesizing detectable amounts of IL-1beta on their own. We suggest that any IL-1beta synthesis detected is a by-product of leukocytes contaminating the platelet preparations. Thus, the hypothesis that platelets producing IL-1beta, provide a new link between thrombosis and inflammation needs to be reconsidered.