Abstract
We have employed zymosan (Z), 1 particle/15 platelets, as an in vitro probe for the study of the effects of immunologic reactions on human platelets. Studies by others had shown a) that human platelets respond with aggregation and release reactions when exposed to Z previously treated with normal plasma; b) that an intact alternative C pathway as well as fibrinogen are required; and c) that the critical plasma reactants are Z bound. Using genetically C-deficient human plasmas, we have previously reported requirements for C5, C6, and C7 but not C8 in the formation of the active Z-complex.
Utilizing agammaglobulinemic (agamma) plasma and washed human platelets, we have demonstrated a requirement for IgG in this reaction. Agamma plasma did not support Z-induced platelet activation, whereas Z previously incubated in normal plasma activated agamma platelets. This agamma plasma defect was corrected by purified normal IgG, but not by F(ab′)2 or Fc fragments.
