Non-reactive SLE sera in an ELISA for anticardiolipin antibody (aCL) retested positive in the immunoassay when the sera were first heat-inactivated at 56 degrees C for 30 minutes. This was not a false positive phenomenon since the positive ELISA reactivity of the heated SLE sera was markedly reduced by inhibition with the cardiolipin antigen. Furthermore, the heat-potentiated ELISA reaction was abolished by prior IgG depletion of the SLE sera with Protein A preparation. The unmasked aCL in the heat-treated SLE sera also exhibited selective binding in ELISA to other negatively-charged phospholipids, namely phosphatidylserine and phosphatidic acid but not against either phosphatidylcholine or phosphatidyl-ethanolamine. The data strongly indicate an interaction between antiphospholipid antibodies and heat-sensitive serum component(s), a reduction of the latter resulting in the ELISA detection of the autoantibody.
Heat-sensitive serum masking cofactor(s) of antiphospholipid antibody (aPL) in normal human sera (NHS) are specifically inactivated at 56 degrees C. The degree of binding in ELISA by unmasked aPL in NHS was equivalent to that in non-heated, aPL-reactive autoimmune SLE sera. Previously "negative" SLE sera also reacted equally strongly in the aPL ELISA when similarly heat-inactivated. Isotype studies by ELISA of the heat-potentiated aPL in 36 NHS revealed the presence of specific IgG (34/36), IgM (11/36) and IgA (24/36) aPL antibodies. 11/36 (31%) NHS had all three aPL isotypes while 13/36 (36%) had both IgG and IgA antibodies to phospholipid.
Normal human sera (NHS), heat-inactivated at 56 degrees C for 30 min, demonstrated positive ELISA reactions for anti-cardiolipin (aCL) antibodies. The heat-induced reactivity in ELISA was inhibitable by the cardiolipin antigen and was abolished by prior IgG depletion of the heated NHS with a protein A preparation. The heat-potentiated aCL also cross-reacted selectively with phosphatidic acid and phosphatidylserine, but not with phosphatidylcholine or phosphatidylethanolamine.
We conducted a prospective longitudinal study to determine the nature and prevalence of cardiac abnormalities in systemic lupus erythematosus and to study their natural history and relationship with disease activity. Forty consecutive inpatients with systemic lupus erythematosus were studied during their admission and subsequently 6 to 12 months later. On each occasion a clinical cardiovascular examination was carried out, disease activity was scored using the "Lupus Activity Criteria Count" and a Doppler echocardiographic examination was carried out. 72.5% of patients had an abnormal echocardiogram in the first study while 51.7% were abnormal during the follow-up study. Valvar disease occurred in 37.5% of patients. The mitral valve was most commonly affected. Libman-Sacks endocarditis was rare (2.5%). Pericardial effusions were seen in 36.2% of echocardiograms. The majority (76.0%) of these were associated with hypoalbuminaemia. 80.0% of patients had active disease during the first examination and 41.4% at follow-up. There was no correlation between activity of disease and prevalence of cardiac abnormalities at either examination. We conclude that cardiac disease is common in systemic lupus erythematosus. Prevalence of cardiac abnormality did not correlate with disease activity.
The anti-phospholipid antibody (aPL) in 26 heat-inactivated normal human sera (NHS) was tested for IgG subclass in ELISA. The specific antibody in NHS included all four IgG antibody subclasses, as well as IgA. The incidence of IgG subclasses ranged from 50% (13/26) for IgG1 to 92% (24/26) for IgG2. Specific IgA anti-phospholipid antibody (aPL) was detected by ELISA in 38% (28/73) of normal human saliva. The salivary IgA aPL bound preferentially to anionic phospholipids including cardiolipin, phosphatidylserine and phosphatidic acid but not to phosphatidylcholine or sphingomyelin. Unlike aPL in normal human sera, aPL in saliva was predominantly not associated with the previously described heat-labile inhibitor of aPL. This may indicate a role of salivary IgA aPL in local immunity by binding to cross-reactive bacterial cell surface components including phospholipids.