Why do patients with antiphospholipid antibody clot?

Antiphospholipid antibodies and the risk of thromboembolic events in valvular heart disease

OBJECTIVE

To investigate the role of antiphospholipid antibodies (aPLs) in subsequent thromboembolic events and mortality in a prospective follow-up of 89 patients with severe, nonspecific valvular heart disease.

PATIENTS AND METHODS

Between November 1, 1993, and March 31, 1994, 89 patients with valvular heart disease were assessed for the presence of anticardiolipin antibodies and lupus anticoagulant. The primary end point was thromboembolic events, and the secondary end points were cardiovascular mortality and overall mortality.

RESULTS

All patients were followed up for a mean of 59 months; 1 patient (without aPLs) was lost to follow-up. Nineteen patients had increased titers of aPLs. Thromboembolic events were significantly more frequent in the aPL-positive group than in the aPL-negative group (7/19 [37%] vs 8/70 [11%]; P=.01). Cardiovascular mortality tended to be higher in the aPL-positive group than in the aPL-negative group (3 [16%] vs 6 [9%]; P = .40). However, in multivariate Cox analysis, presence of aPLs was not an independent risk factor for thromboembolic events.

CONCLUSION

Our results suggest that patients with severe valvular heart disease and aPLs have an increased risk for developing thromboembolic events.

Antimalarial drugs in systemic lupus erythematosus: use in pregnancy

The 4-aminoquinoline radical containing antimalarial drugs are also used in the management of various connective tissue diseases including systemic lupus erythematosus (SLE) and rheumatoid arthritis. These agents are particularly useful for the management of inflammatory polyarthritis and skin disease. By raising the pH in intracellular compartments, these drugs interfere with normal phagocytic function which consequently enables them to interfere with antigen processing. Other actions include inhibition of platelet aggregation, this is advantageous in patients with phospholipid antibodies (aPL) which are known to predispose patients to recurrent arterial and venous clinical thrombotic events. Hydroxychloroquine has also been demonstrated to reduce serum lipid levels including cholesterol, triglycerides and low density lipoproteins. As it is now known that patients with SLE are at risk for accelerated artherogenesis and premature heart disease, this action may be an added benefit for these patients. The use of the 4-aminoquinoline radical containing antimalarial drugs during pregnancy is controversial. It is known that these agents can cross the placenta and are deposited in fetal pigmented tissues. These findings have led to the recommendation that these agents should be discontinued in pregnancy for patients with connective tissue diseases even though they have long been recommended for malarial prophylaxis in pregnant women travelling to malarial infested areas. Flares of SLE disease have been documented when these agents are discontinued and as flares of SLE disease activity are known to be detrimental to pregnancy outcome in patients with SLE, it is our opinion that these drugs should not be discontinued during pregnancy in a patient with lupus, particularly when the known terminal elimination half life is 1 to 2 months.

The effects of a human IgM monoclonal anticardiolipin antibody on pregnancy in a transgenic mouse model

The clinical features of antiphospholipid (or Hughes') syndrome (APS) are most commonly seen in individuals who have raised levels of IgG anticardiolipin antibodies. Most murine models of the syndrome have involved the administration of such antibodies to normal mice. However, APS can occur in the presence of raised levels of serum IgM anticardiolipin antibodies alone. The present study was designed to see if an IgM monoclonal antibody can induce changes in mice similar to those seen in human APS. This antibody, BH1, has previously been derived from a patient with primary APS. In its ligand-binding and idiotypic characteristics it is representative of antiphospholipid antibodies (aPL) found in the serum of patients with APS. In order to minimise the immune response to human IgM, we used transgenic mice (F15) which express, and are predicted to be tolerant of, human immunoglobulin mu chains. The features of APS may develop more readily in individuals who have an existing autoimmune disorder, such as systemic lupus erythematosus (SLE). We therefore crossed these transgenic mice with New Zealand Black (NZB, SLE-prone) mice, and used the progeny (F15 x NZB/F1) in our experiments. Twenty-four F15 x NZB/F1 mice were given BH1, or a control IgM antibody, (A5566) immediately preceding and then three times during pregnancy. There was a reduction in the mean number of foetuses in animals given BH1 compared with those given A5566 (8.6 vs 11.0; P < 0.05), and a similar reduction in mean total foetal weight per pregnancy (9.05 vs 12.73 g; P < 0.05). Two mice showed a marked reduction in platelet count. No evidence of thrombosis was detected macroscopically or histologically. Our results show a lower incidence of APS-type features compared to previous studies in which mice have been administered aPL. This may be because BH1 is an IgM antibody. Nevertheless, the data support the concept that IgM aPL of particular ligand-binding specificities may have a direct pathogenetic role in certain cases of human APS.

Association between anticardiolipin antibodies and mortality in patients with peripheral arterial disease

PURPOSE

Anticardiolipin antibodies may be associated with recurrent thromboembolic events in patients with myocardial infarction or stroke. We sought to determine the prevalence of anticardiolipin antibodies in patients with peripheral arterial disease and their association with subsequent thromboembolic events and mortality.

METHODS

We ascertained anticardiolipin antibodies using a standardized enzyme-linked immunosorbent assay (immunoglobulin G [IgG] anticardiolipin > or =15 GPL units or IgM anticardiolipin > or =15 MPL units) in 232 patients with peripheral arterial disease and 100 control subjects. Patients were observed to determine overall and cardiovascular mortality, and incident thromboembolic events.

RESULTS

IgG anticardiolipin antibodies were significantly more common in the patients with peripheral arterial disease (36 of 232 [16%]) than in the controls (7 of 100 [7%], P = 0.03). During a median follow-up of 3.5 years, 3 of the 232 patients were lost to follow-up and 56 (24%) died. Overall mortality was significantly greater in the IgG anticardiolipin-positive patients (16 of 35 [46%]) compared with those who were IgG anticardiolipin-negative (40 of 194 [21%], P = 0.0003), largely due to an increase in cardiovascular mortality among the IgG anticardiolipin-positive patients. In a multivariate proportional hazards analysis, IgG anticardiolipin antibodies were an independent risk factor for overall mortality (hazard ratio [HR] = 2.1, 95% confidence interval [CI]: 1.2 to 4.0) and cardiovascular mortality (HR = 4.4, 95% CI: 1.6 to 12).

CONCLUSIONS

IgG anticardiolipin antibodies are common in patients with peripheral arterial disease and are associated with an increased risk of overall and cardiovascular mortality.