Summary
The ability to readily identify dead platelets is invaluable to studies examining
the means of their death, factors affecting their lifespan and their means of clearance
by phagocytes. The aim of the present work was to develop a vital staining procedure
for the rapid and objective discrimination of live from dead platelets that accrued
in citrated platelet rich plasma (cPRP) incubated at 37°C for several days. By transmission
electron microscopy it was noted that platelet death was morphologically similar to
necrosis and associated with aggregate formation. The vital dyes calcein-AM and FM
4–64 were found to robustly report the death of platelets and indicated that the aggregates
which formed during incubation were populated exclusively by dead platelets. Additionally,
platelet death was associated with the shedding of CD42b. Microscopic and cytometric
analyses of incubated cPRP indicated that shedding of CD42b and aggregate formation
by dead platelets were completely inhibited by the metalloproteinase inhibitor GM6001.
Automated counting of platelets incubated in the presence of GM6001 revealed that
death did not lead to a loss in cellularity. It is proposed that calcein-AM and FM4–64
are effective as vital stains for the reliable assessment of platelet viability and
that platelet aggregation can occur by a novel mechanism dependent upon platelet death
and metalloproteinase activity.
Keywords
Platelets - death - metalloproteinase - agglutination - cytometry