Role of beta 2-glycoprotein I in the anticardiolipin antibody affinity for phospholipid in autoimmune disease.

The binding capacity to cardiolipin and the functional affinity of affinity-purified anticardiolipin (aCL) IgG of patients with autoimmune disease have been compared with those of individuals with malaria and acquired immunodeficiency syndrome (AIDS). The binding of autoimmune IgG aCL was enhanced gradually by the incorporation of increasing amounts of beta 2-glycoprotein I (beta 2GPI) into the assay, in contrast to that of patients with infectious diseases. In addition, there were significant reductions of functional affinity in autoimmune disease, but not in malaria or in AIDS. These results indicate that beta 2GPI requirement for binding to the target antigen varies inversely with functional affinity in autoimmune disease when beta 2GPI was present, and suggest that IgG aCL are more heterogeneous in this type of disorder than in patients with infectious disease.