A randomized clinical trial of high-intensity warfarin vs. conventional antithrombotic therapy for the prevention of recurrent thrombosis in patients with the antiphospholipid syndrome (WAPS)

BACKGROUND

The optimal intensity of oral anticoagulation for the prevention of recurrent thrombosis in patients with antiphospholipid antibody syndrome is uncertain. Retrospective studies show that only high-intensity oral anticoagulation [target international normalized ratio (INR) >3.0] is effective but a recent randomized clinical trial comparing high (INR range 3.0-4.0) vs. moderate (INR 2.0-3.0) intensities of anticoagulation failed to confirm this assumption.

METHODS

We conducted a randomized trial in which 109 patients with antiphospholipid syndrome (APS) and previous thrombosis were given either high-intensity warfarin (INR range 3.0-4.5, 54 patients) or standard antithrombotic therapy (warfarin, INR range 2.0-3.0 in 52 patients or aspirin alone, 100 mg day(-1) in three patients) to determine whether intensive anticoagulation is superior to standard treatment in preventing symptomatic thromboembolism without increasing the bleeding risk.

RESULTS

The 109 patients enrolled in the trial were followed up for a median time of 3.6 years. Mean INR during follow-up was 3.2 (SD 0.6) in the high-intensity warfarin group and 2.5 (SD 0.3) (P < 0.0001) in the conventional treatment patients given warfarin. Recurrent thrombosis was observed in six of 54 patients (11.1%) assigned to receive high-intensity warfarin and in three of 55 patients (5.5%) assigned to receive conventional treatment [hazard ratio for the high intensity group, 1.97; 95% confidence interval (CI) 0.49-7.89]. Major and minor bleeding occurred in 15 patients (two major) (27.8%) assigned to receive high-intensity warfarin and eight (three major) (14.6%) assigned to receive conventional treatment (hazard ratio 2.18; 95% CI 0.92-5.15).

CONCLUSIONS

High-intensity warfarin was not superior to standard treatment in preventing recurrent thrombosis in patients with APS and was associated with an increased rate of minor hemorrhagic complications.

Role of cyclic nucleotides in human lymphocyte-mediated antibody-dependent cytotoxicity

Experiments were carried out in order to throw light on the role of cyclic AMP and cyclic GMP in the modulation of the expression of antibody-dependent cytotoxicity mediated by human peripheral blood lymphocytes in vitro. Chicken erythrocytes were used as target cells. Support for an inhibitory role of cyclic AMP was derived from the marked suppression of cytotoxicity by dibutyryl cyclic AMP. Cyclic AMP itself had little effect. Isoproterenol, prostaglandin E1 and prostaglandin E2 increased cyclic AMP concentrations and strongly inhibited the cytotoxic effect of the lymphocytes. Histamine showed very slight elevation of the cyclic AMP level and suppression of the cytotoxicity. Theophylline did not increase the cyclic AMP concentration, but potentiated the effects of isoproterenol and prostaglandin E1 on the cyclic AMP levels, and significantly inhibited cytotoxicity. No clear effects were seen when cyclic GMP, dibutyryl GMP, acetylcholine or carbacholine were added to the cells. The results indicate that in this system cyclic AMP inhibits cytotoxicity, while no evidence for a role of cyclic GMP has been obtained.

Abnormal lymphocyte populations in pure red cell aplasia

Studies of blood lymphocytes from 4 patients with pure red cell aplasia were performed with lymphocyte surface markers, and with various in vitro tests for lymphocyte functions. Pathologically low B-lymphocyte values were found. In contrast, no marked deviation from normals were seen for T-lymphocytes and Fc-receptor-bearing lymphocytes thought largely to represent non-B, non-T-lymphocytes. In 3 patients normal lymphocyte transformation was found with unspecific and specific mitogens, while the DNA-synthesis induced by unspecific mitogens was subnormal in the fourth patients. The lymphocyte-mediated PHA-induced cytotoxicity against target cells in vitro was subnormal in 2 patients, while no depression was seen in antibody-dependent cytotoxicity mediated in vitro by lymphocytes (K-cells). It is concluded that considerable immunological abnormalities are associated with pure red cell aplasia, and the possible significance of this is discussed.

Different lymphocyte populations in rheumatoid arthritis and their relationship to anti-Ig activities

The anti-immunoglobulin activities of rheumatoid arthritis appear to be related not only to plasma cells and their precursors, the B-lymphocytes. Evidence for interaction of IgG with T-lymphocytes and with Fc-bearing lymphocyte-like cells has now appeared. Both these cell types can mediate cytotoxicity which may also induce inflammation in addition to that provoked by rheumatoid factors and immune complexes. Rheumatoid factors and immune complexes may act primarily through the complement system. However, active inflammation in rheumatoid patients can occur without abundant immune complexes, e.g. in B-cell-deficient patients (31). In some cases this may be due to activation of the alternate complement pathway. However, the T-cell system with its series of lymphokines may also play an active part-in the inflammatory process. And both T-lymphocytes and Fc-bearing lymphocyte-like cells, the K-cells, can mediate cytotoxicity. Also in such patients further studies are needed to work out the complex interactions between these cell types and to discover the underlying cause or agent in the chronic destructive rheumatoid inflammation.

Structural requirements in the Fc region of rabbit IgG antibodies necessary to induce cytotoxicity by human lymphocytes

Rabbit IgG anti-chicken erythrocyte antibodies were compared with the Fab/c or Facb fragments of IgG and with partially reduced and alkylated IgG for the capacity to induce cytotoxicity by normal human lymphocytes. The Fab/c antibody fragment, which lacks one Fab region, was still able to induce cytotoxicity. In contrast, the Facb antibody fragment, which lacks the C-gamma3 domains, was nearly ineffective in activating the effector cells, whereas intact antibody activity was demonstrated by its ability to inhibit the cytotoxicity induced by unsplit IgG. Similarly, partial reduction and alkylation of the IgG antibodies, under conditions affecting the interchain disulphide bonds only, greatly diminished their ability to induce cytotoxicity, although they effectively inhibited the cytotoxicity induced by untreated IgG. On the basis of these results and previous data, we suggest that the reaction of the Fc region of IgG with the effector cell depends on the integrity of the C-gamma2 domain in the native, divalent state or on the interaction between the C-gamma2 and C-gamma3 domains.

Antibody-dependent cytotoxicity mediated by human Fc-receptor-bearing cells lacking markers for B- and T-lymphocytes

The effector cell in human antibody-dependent cytotoxicity was studied by means of various cell fractionation methods. A strong decrease of cytotoxicity was observed in cell suspensions depleted of lymphocytes forming rosettes with human erythrocytes sensitized with human IgG (EA-RFC) either by gradient centrifugation of rosettes or by fractionation on immune complex Degalan columns. The EA-RFC-depleted, ineffective cell suspensions contained considerable proportions of Ig-positive lymphocytes. In contrast, a marked increase in both cytotoxicity and the proportion of EA-RFC was observed after depletion of T-lymphocytes forming rosettes with sheep erythrocytes by gradient centrifugation. The net effect of the presence of monocytes was to diminish cytotoxicity as measured by chromium release, probably because phagocytized target cells were protected from extracellular lysis. It is concluded that antibody-dependent cytotoxicity in man is mediated by a lymphocyte-like cell that has receptors for the Fc part of IgG but lacks conventional B- and T-lymphocyte markers.

Characterization of subpopulations of human lymphoid cells participating in phytohemagglutinin and concanavalin A-induced cytotoxicity

The cells participating in phytohemagglutinin (PHA) and concanavalin A (Con A) induced cytotoxicity mediated by human lymphoid cells were studied by means of various cell fractionation methods. A considerable decrease of cytotoxicity induced by these mitogens was observed in cell suspensions depleted of T lymphocytes forming rosettes with sheep erythrocytes, by gradient centrifugation. Also, depletion of Fc-receptor-bearing lymphoid cells, either by gradient centrifugation or by fractionation on immune complex Degalan columns, led to a marked reduction of the cytotoxic response to PHA and Con A. Our data indicate that optimal cytotoxicity induced by activation with PHA or Con A requires the presence of least two populaitons of lymphoid cells, of thymus as well as non-thymus origin.

Human lymphocytes with receptors for IgG. A population of cells distinct from T- and B-lymphocytes

Human lymphocytes with receptors for IgG (EA-RFC) were detected in peripheral blood by their ability to form rosettes with human erythrocytes sensitized with human (Ripley anti-CD) or rabbit IgG. EA-RFC were shown to be different from T-lymphocytes forming rosettes with sheep erythrocytes (E-RFC), both by direct studies of mixed rosette suspensions and by separation of EA-RFC and E-RFC by depletion of either EA-RFC or E-RFC by gradient centrifugation of the corresponding rosettes, as well as by fractionation of cells on HSA/anti-HSA columns, which very effectively and selectively retain EA-RFC. Proportions of EA-RFC were also within the normal range in patients with profound lack of T-cells and were not increased during <i>in vitro </i>lymphocyte culture in the presence of T-cell mitogens. The majority of EA-RFC was also distinct from B-lymphocytes as identified by membrane-bound Ig. Thus, EA-RFC could be separated from B-lymphocytes by fractionation on nylon columns retaining B-lymphocytes, but not EA-RFC, by fractionation on HSA/anti-HSA columns retaining EA-RFC but not B-lymphocytes, as well as by depletion of EA-RFC by gradient centrifugation of rosettes. The correlation between EA-RFC and B-lymphocytes in blood was also very poor, both in patients with pathologically low proportions of either normal or malignant B-lymphocytes as well as with abnormally high proportions. It is therefore concluded that EA-RFC represent a population of lymphocytes largely unrelated to human T- and B-lymphocytes as identified by conventional markers.