Detection and significance of alpha granule membrane protein 140 expression on platelets collected by apheresis.

Activation of platelets may be measured by using the monoclonal antibody S12 to detect alpha granule membrane protein 140 (GMP-140) antigen expressed only on activated platelets. S12 was used to measure activation of apheresis platelet concentrates by flow cytometry. Eleven platelet concentrates obtained by one method and nine obtained by another were analyzed 4 hours after collection. Means +/- 1SD of 25.3 +/- 14.8 percent and 28.9 +/- 11.6 percent, respectively, of platelets were found to be activated (range, 4.8-53.1%). Six of the platelet concentrates obtained by the second method were filtered. There was a drop of 17.8 percent (range, 10-25%) in the mean total number of platelets recovered after filtration, but there was no difference in the proportion of activated platelets measured immediately before and after filtration. The 1-hour posttransfusion platelet count increment was obtained after 12 of these apheresis platelet concentrates were transfused to eight patients who were not refractory from either a clinical or alloimmune standpoint. There was a significant inverse correlation between the platelet count increment and the proportion of activated platelets in the component (p less than 0.05, r = -.58). These data suggest that apheresis platelet concentrates with more activated platelets have a reduced 1-hour recovery. Filtration did not enhance activation or selectively remove activated platelets. Expression of GMP-140 may serve as a useful quality control measurement.