Spreading of wt and SAP^–/– platelets on the immobilized extracellular domain of CD84. Graphic representation of wt (n = 5) and SAP^–/– (n = 5) washed mouse platelet spreading on the indicated surfaces in the presence or absence of added 1 μM ADP or 100 μM MRS2179. **, P < .01; ***P < .005.