We evaluated the clinical significance of aPT and aPS-PT by testing for the presence of these antibodies in 212 SLE patients and in 100 healthy individuals. Results show that anti-prothrombin antibodies were found in 47% of the patients (aPT in 31% and aPS-PT in 31%). Their presence did not correlate with that of aCL, anti-beta2GPI, LA and/or anti-protein S. IgG but not IgM aPT were more frequently found in patients with thrombosis than in those without. IgG and IgM aPS-PT were also more frequent in patients with thrombosis (venous and/or arterial) than in those without. Levels of IgG aPT and IgG and IgM aPS-PT were higher in patients with thrombosis than in those without. Although aPT and aPS-PT were more frequently found in women with adverse obstetric history than in those without, the differences were not statistically significant. More significantly, 48% of the patients with aPL-related clinical features who were negative for standard tests had antiprothrombin antibodies. We can conclude that aPT and aPS-PT are frequently found in SLE. Their presence is associated with thrombosis, making these antibodies potential markers for the APS. Testing for these antibodies could be of clinical benefit in patients who are negative for the routinely used tests.

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Objective. To determine whether immunoglobulins with affinity for the vascular endothelium displayed any distinguishing behavior during normal and systemic lupus erythematosus (SLE) pregnancy. We also attempted to verify whether isotype expression of antiendothelial cell antibodies (AECA) would have any predictive value for pregnancy outcome.Methods. Sera from 38 pregnant patients with SLE, 68 normal pregnant women, and 84 nonpregnant healthy controls were studied. IgM-and IgG-AECA were determined by cellular enzyme-linked immunosorbent assay using fixed cultured human umbilical vein endothelial cells. Results. A significantly higher level of IgM-AECA was found during normal pregnancy compared with that in healthy nonpregnant controls (mean ؎ SD 39 ؎ 12% versus 21 ؎ ؎ ؎ 12%; P < < < 0.0001). Most pregnant patients with SLE did not have increased titers of IgM-AECA, but instead had levels similar to those found in healthy nonpregnant controls (23 ؎ 12%; P not significant). The lowest levels of IgM-AECA in lupus pregnancy were associated with preeclampsia (odds ratio 16, P < 0.005). Conversely, IgG-AECA levels were significantly higher in the serum of normal pregnant women and pregnant SLE patients than in the serum of healthy nonpregnant controls (24 ؎ 7% and 24 ؎ 14% versus 9 ؎ 7%; P < 0.0001). Conclusion. Our results indicate that an activeimmune response occurs during pregnancy. This response involves increased activity of AECA, suggesting a role of autoantibodies as a possible contributing factor toward fetal tolerance. Our observations further indicate that impaired immune regulation, such as diminished levels of serum IgM-AECA detected in SLE patients, might contribute to the impaired reproductive function commonly found in SLE.

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