Enrichment of antibodies against phospholipids in circulating immune complexes (CIC) in the anti-phospholipid syndrome (APLS)

The aim of this study was to analyse and characterize immunoglobulins in CIC and serum from patients with anti-cardiolipin antibodies. CIC from five patients were isolated by gradient centrifugation and gel filtration. The distribution between serum and CIC of immunoglobulin reactivity against different phospholipids was determined. Serum and CIC contained antibodies against cardiolipin and other negatively charged phospholipids. The relative concentration of these antibodies was higher in the immune complexes than in corresponding sera, and the avidity of antibodies in immune complex form was higher. The presence of high concentrations of antibodies to negatively charged phospholipids in CIC iom patients with anti-cardiolipin antibodies could be of pathogenic significance in APLS by conferring characteristics to the complexes of importance for binding to membrane components. This could have special implications with regard to platelet and complement activation, thrombocytopenia and thrombophilia.