Summary
1. Provided they are coated with gammaglobulin, polystyrene latex particles induce
in washed human blood platelets the release of adenine nucleotides, aggregation and
the contraction of the formed aggregates. Albumin and fibrinogen are unable to replace
gammaglobulin in this reaction. Particles with a diameter of about 0.8 μ proved most
effective; larger ones were inactive.
2. The release of nucleotides is a fast process; it is impaired but not completely
inhibited by the removal of Ca++-ions. Aggregation and contraction of the aggregates
are absent without Ca++-ions.
3. Normal gammaglobulin by itself has scarcely an effect upon platelets and it fixes
added hemolytic complement (C’) only to a negligible extent. After the adsorption
to latex it acquires strong C’-fixing properties, and becomes more reactive towards
platelets. Repeated adsorption of the same gammaglobulin preparation with latex did
not change this behaviour, which therefore is due to a property of the gammaglobulin
itself, and not of a preferentially adsorbed, C’-activating contaminant. Treatment
at pH 4 of gammaglobulin before its adsorption onto latex simultaneously abolished
its effects on platelets, and on C.
4. It must be concluded that the effect of opsonized latex particles upon blood platelets
is unseparable from their C’activating capacity. On the other hand, the addition of
C’ not only proved unnecessary; the presence of serum rather impaired the release
of nucleotides by latex particles.
