A subset of patients with systemic lupus erythematosus has autoantibodies to acidic phospholipids. Since lipids are poor immunogens, the mechanism responsible for the induction of these antibodies is unclear. Immunization of a normal rabbit and normal mice with purified human g62-glycoprotein I (apolipoprotein H) resulted in the production of high levels of two non-cross-reactive antibody populations, anti-apolipoprotein H, and antiphospholipid. The antiphospholipid antibodies had binding specificities indistinguishable from autoantibodies obtained from human and murine lupus. These findings suggest a novel mechanism for the induction ofantiphospholipid autoantibodies. (J. Clin. Invest. 1992. 90:1105-1109

Antiphospholipid antibodies (aPL) are associated with a syndrome of arterial and venous thrombosis and recurrent fetal loss. We have shown that IgG purified from patients with aPL activate vascular endothelial cells (EC), converting the steady-state, non-thrombotic endothelial surface to a pro-thrombotic state. The aPL-activated EC are characterized by the expression of leukocyte adhesion molecules, including ICAM-1, VCAM, and E-selectin. EC activation is dependent upon the presence of beta 2-GP-I, a cofactor necessary for anticardiolipin reactivity. In addition, EC activation is not attributable to endotoxin contamination, Fc receptor interactions, or immune complexes, but rather is the result of the specific anticardiolipin reactivity of the IgG. Endothelial activation by aPL may be an important mechanism by which these antibodies cause a hypercoagulable state.

Contraceptive choice in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) is challenging but important. Long-acting forms of contraception such as the progesterone intrauterine device (IUD) or subdermal implant are preferable for most patients. Estrogen-containing hormonal contraceptives may be used in stable, inactive SLE patients but are contraindicated in patients with positive antiphospholipid antibodies (aPL). The levonorgestrel IUD is a good alternative for many APS patients and often decreases menstrual blood loss. It is prudent to avoid depot medroxyprogesterone acetate (DMPA) in corticosteroid-treated or other patients at risk for osteoporosis because of the inhibition of ovulation. Effective and safe contraception in patients with SLE and APS permits planning for pregnancy during inactive disease and while on pregnancy-compatible medications, preventing a poorly timed pregnancy that may jeopardize maternal and/or fetal health.

Human immunoglobulin G (IgG) is comprised of four subclasses with distinct structural and biologic properties. Patients with autoimmune disease, in general, show an overall increase in serum IgG as well as skewing in subclass distribution for particular autoantibodies. Antinuclear antibodies and anti-double stranded DNA antibodies, for example, are primarily IgG1 and IgG3. In contrast, anticardiolipin antibodies show a skewing towards presence of IgG2 presence is associated with arterial and venous thrombotic complications. Selective absorption of IgG2 from high titer sera abrogates aCL ELISA binding. Pathogenicity of aCL may be related to IgG2 in an important way. The precise mechanism of action and nature of the inducing stimulus are not yet clear.