Platelets, Arthus-type reactions and inflammatory mediators.

The release of inflammatory mediators and the appearance of necrohaemorrhagic lesions induced by subcutaneous implantation of sponges containing antiplatelet serum globulins were studied in control and thrombocyto-penic rats. In thrombocytopenic animals, antiplatelet globulins caused a greater release of prostaglanding-like material and 5-hydroxytryptamine as well as larger inflammatory lesions. Thus, platelet integrity is not necessary for the induction of lesions by antiplatelet globulins and the mediators in the sponge exudates must have originated from leucocytes or damaged tissues. Mast cells seem not to be involved in the production of 5-hydroxytryptamine in this inflammatory reaction. It is suggested that in idiopathic thrombocytopenic purpura (ITP) an Arthus-type hypersensitivity reaction, rather than the thrombocytopenia itself, is the cause of the vascular lesions and their manifestations.