beta2-glycoprotein I (beta2-GPI) mRNA is expressed by several cell types involved in anti-phospholipid syndrome-related tissue damage

Anticardiolipin antibodies (aCL) in the sera of patients with antiphospholipid syndrome (APS) recognize an altered structure of beta 2-glycoprotein I (beta 2-GPI) interacting with solid-phase negatively charged phospholipids. beta 2-GPI bound to Cu2+-oxidized plasma lipoproteins, i.e. oxidized very low-density lipoprotein (oxVLDL), oxidized low-density lipoprotein (oxLDL), or oxidized high-density lipoprotein (oxHDL). beta 2-GPI inhibited in vitro uptake, i.e. cell surface binding, cellular association, and proteolytic degradation of oxLDL by murine macrophage J774A.1 cells. The binding of oxLDL to the macrophages was inhibited by the addition of polyinosinic acid (poly (I)), a competitor of the scavenger receptor, but not by another polyanionic acid, polycytidylic acid (poly (C)). Conversely, the binding of oxLDL was significantly increased by the simultaneous addition of human beta 2-GPI and monoclonal aCL derived from NZW x BXSB F1 (WB F1) mice, an animal model of APS, or anti-beta 2-GPI antibodies from BALB/c mice immunized with human beta 2-GPI. These findings indicate that beta 2-GPI may be an antiatherogenic protein and that the autoimmune response against beta 2-GPI may have a role in the development of atherosclerosis in APS.

The validity of the hypothesis that some of the neuropsychiatric manifestations of systemic lupus erythematosus (SLE) are mediated by the direct effects of antibody binding to neuronal cell membranes is dependent on the demonstration of antineuronal activity within the central nervous system of patients with active central nervous system disease. Using a radiolabelled staphylococcal protein A assay, we tested cerebrospinal fluid from 27 patients with SLE and central nervous system manifestations, and cerebrospinal fluid from 18 additional patients with SLE but free of central nervous system disease for antibody reactive with the cultured human neuronal cell line SK-N-SH. Cerebrospinal fluid from 20 of 27 patients with active lupus central nervous system disease had increased immunoglobulin G (IgG) antineuronal activity compared with cerebrospinal fluid from two of 18 patients with SLE without central nervous system disease. Ninety percent of the patients with psychosis, organic brain syndrome or generalized seizures had increased IgG antineuronal activity as compared with only 25 percent of the patients who presented with hemiparesis or with chorea/hemiballismus. Antineuronal activity per microgram of IgG was concentrated eightfold in the cerebrospinal fluid of patients with active central nervous system disease as compared with the serum activity. Patients with or without active central nervous system disease did not differ significantly in the amount of serum antineuronal binding activity. The results are consistent with the hypothesis that the more diffuse central nervous system manifestations of SLE are a direct result of the interaction of antibody with neuronal cell membranes.