ACTIVATED HUMAN PLATELETS EXPRESS BETA-2 INTEGRIN

The expression of molecules of the beta 2 integrin family (CD11a, CD11 b, CD11c and CD18) was explored on 2 human megakaryocytic cell lines a nd on platelets from different donors by immunofluorescence and flow c ytometry using a large panel of mAb. CD11a, CD11b, CD11c and CD18 were detected on the megakaryocytic cell lines DAMI and HEL. A low and var iable expression of CD11a, CD11b and CD18 determinants was also detect ed on resting platelets: this expression was markedly increased when p latelets were activated by thrombin. Expression of CD18 was closely co rrelated to that of CD11a or CD11b when comparing the fluorescence int ensity observed in different experiments. In presence of Ca++, platele ts did bind to a RAJI cell line which exhibits a high expression level of CD54. This binding was increased when platelets were activated by thrombin and was decreased by an anti CD11a, CD18 and anti CD54 mAb. T his study indicates that human platelets express molecules of the beta 2 integrin family, when activated, which allows them to bind to CD54 bearing cells.