Summary
The effects on washed human blood platelets of heterologous antiplatelet antiserum, antigen-antibody complexes, and aggregated human gammaglobulin have been compared with those of thrombin. The following results were obtained:
1. Heat-aggregated gammaglobulin and antigen-antibody complexes affected platelets in much the same way as does thrombin; they caused release of adenine nucleotides, aggregation, and contraction of the formed aggregates. Their effect is not inhibited by the presence of hirudin.
2. Anti-platelet antisera (rabbit) gave rise to similar reactions of the platelets, whereby quantitative differences between individual antisera were evident.
3. Release of nucleotides by all types of agents tested is a fast process; at 37° C the major part is released during the first minute.
4. Whereas Ca++-ions are essential for aggregation and concentration of the aggregates, their presence is not necessary for the release-reaction induced by immune agents or thrombin.
5. Calculated on a protein basis, thrombin is twice as efficient as a nucleotide releaser as heat-aggregated gammaglobulin; on a molecular basis, therefore, the gammaglobulin-preparation is more effective.
6. Only immune agents capable of activating the complement system exert an influence on platelets; but neither is the addition of complement necessary, nor was it possible to detect complement on or in the platelets. The possibility is discussed that platelets might possess receptors capable of reacting with C’-activating immune agents, and that this represents a type of cellular reaction which is independent of the activation of plasmatic complement.
