Detection of anticardiolipin antibodies in heat-inactivated normal human sera is not influenced by beta 2-glycoprotein-I

Hidden anti-phospholipid antibodies in normal human sera circulate as immune complexes whose antigen can be removed by heat, acid, hypermolar buffers or phospholipase treatments

Heat treatment of normal human serum reveals otherwise masked anti-cardiolipin antibodies (aCL). We studied the mechanism of masking and the nature of the inhibitor of these aCL IgG. Other forms of treatment, besides heating for 30 min at 56 degrees C, can also unmask hidden aCL IgG. These include acid pH, hypermolar buffers and phospholipase digestion. When unmasked, these aCL recognize other anionic and zwitterionic phospholipids, but do not react with DNA, cell antigens or IgG. Using thin layer chromatography we demonstrate that the heat-labile inhibitor(s) of these aCL are phosphatidylserine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. These antibodies are not beta2-glycoprotein-I dependent and actually compete with this protein for phospholipid binding. The hidden antibodies are comprised of two populations of IgG autoantibodies: one reactive with cardiolipin, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, phosphatidylethanolamine and sphingomyelin, and the other reactive almost exclusively with phosphatidylcholine and phosphorylcholine on enzyme-linked immunosorbent assay plates or when exposed by bromelain on the erythrocyte surface. Our data suggest that hidden aCL are natural oligoreactive IgG anti-phospholipid autoantibodies that circulate masked by their antigen.

Human anticardiolipin monoclonal autoantibodies cause placental necrosis and fetal loss in BALB/c mice

OBJECTIVE

To analyze the structure, specificity, and in vivo pathogenetic potential of 2 human anticardiolipin (aCL) monoclonal antibodies (MAb).

METHODS

Human aCL IgG MAb were generated from hybridized Epstein-Barr virus-induced B cell lines from a healthy subject (MAb 519) and from a patient with primary antiphospholipid syndrome (MAb 516). Studies of antigen-binding specificity and analysis of Ig V-gene mutations were carried out. The MAb were independently injected into mated female BALB/c mice, and their effect on pregnancy outcome was compared with that of MAb 57, a highly mutated and antigen-selected human IgG1lambda rabies virus antibody.

RESULTS

Both MAb 519 and MAb 516 utilized minimally mutated V(H)DJ(H) and VkappaJkappa gene segments and bound cardiolipin and other anionic phospholipids in the absence of beta2-glycoprotein I (beta2-GPI). The mice injected with aCL MAb displayed a significantly higher rate of fetal resorption and a significant reduction in fetal and placental weight as compared with those injected with MAb 57. These findings were accompanied by a finding of placental human IgG deposition and necrosis in the aCL MAb-treated animals.

CONCLUSION

The results of this study indicate that human aCL IgG that are beta2-GPI independent can induce pathology.

The concept and classification of antiphospholipid/cofactor syndromes

In 1990, three groups simultaneously reported that putative IgG antibodies to anionic phospholipids were either not directed to phospholipids or at least required beta 2-glycoprotein-I (beta 2-GP-I) for reactivity in vitro. During the same year, our group described a patient with "idiopathic' hemolytic anemia with serum and erythrocyte-bound IgM antibodies to phosphatidylcholine later found to be independent of beta 2-GP-I for antigen recognition. Lately, the field has been expanded considerably with: (1) the description of other potential antigens such as prothrombin for some lupus anticoagulants, (2) the finding of crossreactivity between some antiphospholipid antibodies (aPL) with thrombomodulin, (3) the presence of serum antibodies to beta 2-GP-I (anti-beta 2-GP-I) in patients with SLE and thromboses, (4) the findings that the clinical manifestations of APS in SLE patients associate more strongly with anti-beta 2-GP-I than with aPL, (5) our finding of a group of SLE patients with the clinical manifestations of APS, with negative serum aPL, but with positive anti-beta 2-GP-I, (6) the description of a group of patients with the clinical manifestations of APS, without serum aPL, without serological nor clinical evidence of any autoimmune disease, but with IgG anti-beta 2-GP-I, and (7) the observation that serum anti-phosphatidylethanolamine antibodies detected in some patients with APS require kininogen (alone or complexed with the kininogen-binding protein), prekallikrein and/or factor XI for in vitro reactivity. Thus, there are antibodies that may be considered true aPL; other "aPL' require a protein cofactor for their detection in vitro, at least in the case of beta 2-GP-I it would appear that their epitope is present on the protein proper not on the phospholipid, hence these are pseudo aPL, and a third group of related anti-cofactor autoantibodies that are directed to the protein in the absence of phospholipid. Clearly, the term "antiphospholipid syndrome' has become obsolete. We propose the term "Antiphospholipid/Cofactor Syndromes' to cull the various syndromes.

Tween 20 detaches cardiolipin from ELISA plates and makes anticardiolipin antibodies undetectable regardless of the presence of beta 2-glycoprotein-I

We investigated the effects of polyoxyethylene sorbitan monolaurate (Tween 20) in the detection of IgG anticardiolipin antibodies (aCL) by the CL-beta 2-glycoprotein-I and the standard aCL solid-phase immunoassays. We found that Tween 20 disengages cardiolipin from a variety of microtiter wells rendering aCL undetectable by both methods. Our results agree with a previous report but are discordant with others. We offer rationale that may explain some of the discrepancies. Based in our findings, we do not recommend the use of Tween 20 for the detection of aCL.