Immune complexes and IgG-Fc receptors on human platelets in essential mixed cryoglobulinemia.

An enzyme-linked immunosorbent assay (ELISA) using wells coated with normal platelets has been tested in order to quantitate cell-bound immune complexes (ICs) by measuring the uptake of alkaline phosphatase-conjugated antibodies to IgG in the immune complexes. All patients with essential mixed cryoglobulinemia had levels of serum IgG ICs above control values; a poor accordance was found between levels of ICs detected by this method and those obtained using the conglutinin method. The presence of these complexes was correlated with human platelet aggregation: platelets aggregated in vitro when cryoglobulins with higher IgG/IgM ratio were present. This type of ICs could be critical also for platelet activation and aggregation in vivo.