The Effects of Aggregated Immunoglobulins on Human Blood Platelets in Relation to Their Complement-Fixing Abilities

[摘要] Human immunoglobulin (IgG) coupled with bis-diazo-benzidine (BDB-IgG) is capable of causing a release reaction from platelets in a manner similar to heat-aggregated IgG or antigen-antibody complexes. Various organic solvents, e.g., ethanol and acetone, also produce platelet-stimulating complexes. All these aggregated immunoglobulins caused the fixation of complement (C), although not strictly in parallel to their ability to cause the platelet release reaction.Myeloma proteins from the subclasses IgG1, IgG2 and IgG3, but not IgG4 or IgA, bind C, while all IgG subclasses, including IgG4, stimulate platelets. IgG3 proteins cause a poor release reaction but bind C well.The release reaction induced by human BDB-IgG is inhibited by monomeric IgG but not by bovine IgG or albumin. Partially purified C1 and purified Clq also inhibit the release reaction. The presence of Ca2+ is not required for any of these effects.It is concluded that for an aggregated immunoglobulin to stimulate platelets it is not necessary that it activate the complement enzymes in the classical way, but that either it may interact with a cell-bound Clq-like receptor, or the immunoglobulin possesses distinct, but closely situated, sites for platelet and C activation.

[学科分类] 生物科学（综合）