PREVALENCE OF ANTIBODIES TO CARDIOLIPIN IN CHRONIC ITP AND REACTIVITYWITH PLATELET MEMBRANES

Anti-cardiolipin antibodies (ACLA) have been suggested to play a role in the pathogenesis of thrombocytopenia. When sera from 40 patients wi th chronic idiopathic thrombocytopenic purpura (ITP) were analyzed for AC LA, these autoantibodies were present in 12 (30%). In 4 sera the a ntibody activity was restricted to the IgG or IgM isotype, respectivel y, while 4 of the samples contained both Ige and IgM antibodies. To el ucidate the interaction between platelets and ACLA, we studied the rea ctivity of sera from non-ITP patients with ACLA, with fragmented plate let membranes. None of them had a concurrent platelet deficiency, but sera from 8 (67%) of them showed increased IgG-binding to platelet mem branes. Absorbtion with cardiolipin reduced membrane binding in 6 (50% ). C3 levels were normal, while low C4 values occurred in both groups with significantly lower levels in ACLA-positive patients (p<0.05). Ci rculating immune complexes (CIC) were common in both groups. Conclusio n: The prevalence of ACLA is increased in ITP and sera from non-ITP pa tients with ACLA react with fragmented platelet membranes. This reacti vity is often decreased by absorption with cardiolipin, suggesting tha t ACLA bind to phospholipid epitopes on platelet membranes.